doc: Convert semihosting readme to rST

This converts the semihosting readme to rST. I have tried to make only
cosmetic changes, but I did fix up the first link (which was broken).

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
diff --git a/doc/README.semihosting b/doc/README.semihosting
deleted file mode 100644
index f382d01..0000000
--- a/doc/README.semihosting
+++ /dev/null
@@ -1,38 +0,0 @@
-SPDX-License-Identifier: GPL-2.0+
-/*
- * Copyright 2014 Broadcom Corporation.
- */
-
-Semihosting is ARM's way of having a real or virtual target communicate
-with a host or host debugger for basic operations such as file I/O,
-console I/O, etc. Please see
-http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjjgij.html for more information.
-
-For developing on armv8 virtual fastmodel platforms, semihosting is a
-valuable tool since it allows access to image/configuration files before
-eMMC or other NV media are available.
-
-There are two main ARM virtual Fixed Virtual Platform (FVP) models,
-Versatile Express (VE) FVP and BASE FVP (See
-http://www.arm.com/products/tools/models/fast-models/foundation-model.php)
-The initial vexpress64 u-boot board created here runs on the VE virtual
-platform using the license-free Foundation_v8 simulator. Fortunately,
-the Foundation_v8 simulator also supports the BASE_FVP model which
-companies can purchase licenses for and contain much more functionality.
-So we can, in u-boot, run either model by either using the VE FVP (default),
-or turning on CONFIG_BASE_FVP for the more full featured model.
-
-Rather than create a new armv8 board similar to armltd/vexpress64, add
-semihosting calls to the existing one, enabled with CONFIG_SEMIHOSTING
-and CONFIG_BASE_FVP both set. Also reuse the existing board config file
-vexpress_aemv8.h but differentiate the two models by the presence or
-absence of CONFIG_BASE_FVP. This change is tested and works on both the
-Foundation and Base fastmodel simulators.
-
-The semihosting code adds a command:
-
-  smhload <image> <address> [env var]
-
-That will load an image from the host filesystem into RAM at the specified
-address and optionally store the load end address in the specified
-environment variable.
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 5b42579..3e52053 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -11,6 +11,7 @@
    netconsole
    partitions
    cmdline
+   semihosting
 
 Shell commands
 --------------
diff --git a/doc/usage/semihosting.rst b/doc/usage/semihosting.rst
new file mode 100644
index 0000000..ed16e4d
--- /dev/null
+++ b/doc/usage/semihosting.rst
@@ -0,0 +1,43 @@
+.. SPDX-License-Identifier: GPL-2.0+
+.. Copyright 2014 Broadcom Corporation.
+
+Semihosting
+===========
+
+Semihosting is ARM's way of having a real or virtual target communicate
+with a host or host debugger for basic operations such as file I/O,
+console I/O, etc. Please see `Arm's semihosting documentation
+<https://developer.arm.com/documentation/100863/latest/>`_ for more
+information.
+
+For developing on armv8 virtual fastmodel platforms, semihosting is a
+valuable tool since it allows access to image/configuration files before
+eMMC or other NV media are available.
+
+There are two main ARM virtual Fixed Virtual Platform (FVP) models,
+`Versatile Express (VE) FVP and BASE FVP
+<http://www.arm.com/products/tools/models/fast-models/foundation-model.php>`_.
+The initial vexpress64 u-boot board created here runs on the VE virtual
+platform using the license-free Foundation_v8 simulator. Fortunately,
+the Foundation_v8 simulator also supports the BASE_FVP model which
+companies can purchase licenses for and contain much more functionality.
+So we can, in U-Boot, run either model by either using the VE FVP (default),
+or turning on ``CONFIG_BASE_FVP`` for the more full featured model.
+
+Rather than create a new armv8 board similar to ``armltd/vexpress64``, add
+semihosting calls to the existing one, enabled with ``CONFIG_SEMIHOSTING``
+and ``CONFIG_BASE_FVP`` both set. Also reuse the existing board config file
+vexpress_aemv8.h but differentiate the two models by the presence or
+absence of ``CONFIG_BASE_FVP``. This change is tested and works on both the
+Foundation and Base fastmodel simulators.
+
+Loading files
+-------------
+
+The semihosting code adds a "hostfs"::
+
+  smhload <image> <address> [env var]
+
+That will load an image from the host filesystem into RAM at the specified
+address and optionally store the load end address in the specified
+environment variable.