kselftest/arm64: Add simple hwcap validation

Add some trivial hwcap validation which checks that /proc/cpuinfo and
AT_HWCAP agree with each other and can verify that for extensions that can
generate a SIGILL due to adding new instructions one appears or doesn't
appear as expected. I've added SVE and SME, other capabilities can be
added later if this gets merged.

This isn't super exciting but on the other hand took very little time to
write and should be handy when verifying that you wired up AT_HWCAP
properly.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829154602.827275-1-broonie@kernel.org


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