cmd: Add a command to display the address map

This adds a new command 'addrmap' to display the address map for
non-identity virtual-physical memory mappings.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 09372d4..9169fff 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -14,6 +14,7 @@
 .. toctree::
    :maxdepth: 1
 
+   addrmap
    base
    bootefi
    booti