kselftest/arm64: Add test case for TPIDR2 signal frame records

Ensure that we get signal context for TPIDR2 if and only if SME is present
on the system. Since TPIDR2 is owned by libc we merely validate that the
value is whatever it was set to, this isn't ideal since it's likely to
just be the default of 0 with current systems but it avoids future false
positives.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-tpidr2-sig-v3-4-c77c6c8775f4@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>