Build: Fix arm/mps3/corstone310_fvp build with cmake 3.16.3

ARMClang.cmake in cmake 3.16 only checks CMAKE_SYSTEM_PROCESSOR variable.
In this case if only ARCH is defined in the build, cmake will throw
an error. But, GCC doesn't support the cortex-m85 processor yet. So we
define the cpu type, and check it in the toolchain_GNUARM.cmake file.

Signed-off-by: Dávid Házi <david.hazi@arm.com>
Change-Id: I12e9f9c0085a0fe1c5bd9900df9e4e923ec0629b
4 files changed