docs(build): update GCC to 11.3.Rel1 version

This toolchain provides multiple cross compilers and is publicly
available on https://developer.arm.com/

We build TF-A in CI using:
AArch32 bare-metal target (arm-none-eabi)
AArch64 ELF bare-metal target (aarch64-none-elf)

Change-Id: I94e13f6c1ebe3a4a58ca6c79c1605bd300b372d3
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>

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 >= 11.2-2022.02 (from the `Arm Developer website`_)
+- GCC >= 11.3.Rel1 (from the `Arm Developer website`_)
 - Clang >= 14.0.0
 - Arm Compiler >= 6.18