docs(arm): update docs to reflect rotpk key changes

The hashing algorithm for the rotpk is now HASH_ALG,
not always sha-256. The public development keys are
no longer in the repository and are now generated at
run-time, updates the documentation to reflect this.

Change-Id: Ic336f7aca858e9b6a1af6d6e6dc5f4aa428da179
Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/docs/design/trusted-board-boot.rst b/docs/design/trusted-board-boot.rst
index f10d2e7..f3e094c 100644
--- a/docs/design/trusted-board-boot.rst
+++ b/docs/design/trusted-board-boot.rst
@@ -39,7 +39,8 @@
 
 -  A Root of Trust Public Key (ROTPK), or a hash of it.
 
-   On Arm development platforms, a SHA-256 hash of the ROTPK is stored in the
+   On Arm development platforms, a hash of the ROTPK (hash algorithm selected by
+   the ``HASH_ALG`` build option, with sha256 as default) is stored in the
    trusted root-key storage registers. Alternatively, a development ROTPK might
    be used and its hash embedded into the BL1 and BL2 images (only for
    development purposes).
@@ -330,7 +331,7 @@
 
 --------------
 
-*Copyright (c) 2015-2020, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2015-2024, Arm Limited and Contributors. All rights reserved.*
 
 .. _X.509 v3: https://tools.ietf.org/rfc/rfc5280.txt
 .. _Trusted Board Boot Requirements (TBBR): https://developer.arm.com/docs/den0006/latest