fix(docs): fix typos in v2.5 release documentation

Two issues in documentation were identified after the release.
This patch fixes these typos.

1. Matternhorn ELP CPU was made available through v2.5 release, not
   Matternhorn CPU
2. We had upgraded TF-A to use GCC 10.2 toolchain family and used this
   toolchain for release testing

Change-Id: I33e59bb5a6d13f4d40dbb3352004d5b133431d65
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

docs/change-log.rst

@@ -107,7 +107,7 @@ New Features
             - Cortex_A78C CPU
             - Makalu ELP CPU
             - Makalu CPU
-            - Matterhorn CPU
+            - Matterhorn ELP CPU
             - Neoverse-N2 CPU
 
     - CPU Errata

docs/getting_started/prerequisites.rst

@@ -26,7 +26,7 @@ Toolchain
 |TF-A| can be built with any of the following *cross-compiler* toolchains that
 target the Armv7-A or Armv8-A architectures:
 
-- GCC >= 9.2-2019.12 (from the `Arm Developer website`_)
+- GCC >= 10.2-2020.11 (from the `Arm Developer website`_)
 - Clang >= 4.0
 - Arm Compiler >= 6.0