arch: Add ARMv8-M support

ARMv7-M support arch directory is modified to support both ARMv7-M
and ARMv8-M. The modified directory is renamed from armv7-m to
arm-m. This in turn affects the SCP_ARCHITECTURE cmake flag which
was previuosly set to armv7-m for armv7m targets and now would be
set by arm-m.

The ARMv8-M support does not include the security extension.

This ARMv8-M support includes support for ARMv8-M Mainline and
ARMv8.1-M Mainline.

ARMv8.1-M Mainline is supported by GCC ver 10.1 onwards, the
latest version can be found here:
https://developer.arm.com/tools-and-software/open-source-software


/developer-tools/gnu-toolchain/gnu-rm/downloads
in addition to LLVM ver 13.0.0 onwards and ArmClang ver 6.14 onwards.

Signed-off-by: Ahmed Gadallah <ahmed.gadallah@arm.com>
Change-Id: I7bdac6c80efbb56a0874daad794111376866a46c