kselftest/arm64: signal: Add SME signal handling tests

kselftest/arm64: signal: Add SME signal handling tests

Add test cases for the SME signal handing ABI patterned off the SVE tests.
Due to the small size of the tests and the differences in ABI (especially
around needing to account for both streaming SVE and ZA) there is some code
duplication here.

We currently cover:
 - Reporting of the vector length.
 - Lack of support for changing vector length.
 - Presence and size of register state for streaming SVE and ZA.

As with the SVE tests we do not yet have any validation of register
contents.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419112247.711548-36-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>