kselftest/arm64: Add SME2 coverage to syscall-abi

Verify that ZT0 is preserved over syscalls when it is present and
PSTATE.ZA is set.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-19-f2fa0aef982f@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>