kselftest/arm64: Skip VL_INHERIT tests for unsupported vector types

kselftest/arm64: Skip VL_INHERIT tests for unsupported vector types

Currently we unconditionally test the ability to set the vector length
inheritance flag via ptrace meaning that we generate false failures on
systems that don't support SVE when we attempt to set the vector length
there. Check the hwcap and mark the tests as skipped when it's not present.

Fixes: 2028fe15d632 ("selftests: arm64: Add coverage of ptrace flags for SVE VL inheritance")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220124175527.3260234-2-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>