kselftest/arm64: Add basic FPMR test

Verify that a FPMR frame is generated on systems that support FPMR and not
generated otherwise.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240306-arm64-2023-dpisa-v5-8-c568edc8ed7f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>