kselftest/arm64: Log signal code and address for unexpected signals

If we get an unexpected signal during a signal test log a bit more data to
aid diagnostics.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230620-arm64-selftest-log-wrong-signal-v1-1-3fe29bdaaf38@kernel.org


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