docs(build): update GCC to 13.2.Rel1 version

Updating toolchain to the latest production release version
13.2.Rel1 publicly available on:
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads



We build TF-A in CI using x86_64 Linux hosted cross toolchains:
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* AArch32 bare-metal target (arm-none-eabi)
* AArch64 bare-metal target (aarch64-none-elf)

Change-Id: I9b60728bcb1a48508ccd4fcbe0114b3029509a64
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>