kselftest/arm64: signal: Add test case for SVE register state in signals

Currently this doesn't actually verify that the register contents do the
right thing, it just verifes that a SVE context with appropriate size
appears.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210819134245.13935-6-broonie@kernel.org


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