kselftest/arm64: Add test case for POR_EL0 signal frame records

Ensure that we get signal context for POR_EL0 if and only if POE is present
on the system.

Copied from the TPIDR2 test.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240822151113.1479789-30-joey.gouly@arm.com


Signed-off-by: Will Deacon <will@kernel.org>