docs(build): update GCC toolchain requirement to 14.2.Rel1

Update documentation to reflect the use of GCC version 14.2.Rel1,
the latest production release available at:
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads

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

Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
Change-Id: I4cd2c16fa9daac1ce518d2280169e92562e3766d
1 file changed