kselftest/arm64: Extend vector configuration API tests to cover SME

Provide RDVL helpers for SME and extend the main vector configuration tests
to cover SME.

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/20220419112247.711548-32-broonie@kernel.org


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