[Buildroot] [PATCH 2/4] package/arm-gnu-a-toolchain: new package

arm trusted firmware requires a bare metal toolchain for its build.
Add pre-built cross-compilation ARM-A bare metal toolchain for Arm Cortex-A
family processors to avoid the following build error.

make[3]: arm-none-eabi-gcc: Command not found

pre-built bate metal ARM GNU-A toolchain installs into the host file system folder
/opt/gcc-arm-none-eabi.

https://developer.arm.com/-/media/Files/downloads/gnu-a/9.2-2019.12/binrel/gcc-arm-9.2-2019.12-x86_64-arm-none-eabi.tar.xz

Signed-off-by: Suniel Mahesh <redacted>

Hi,

Could you please clarify why a separate toolchain is required to build
ATF for this platform ? Is there any specific requirements other than
this particular build error ?

Regards,
Sergey