selftests: arm64: Verify that all possible vector lengths are handled

As part of the enumeration interface for setting vector lengths it is valid
to set vector lengths not supported in the system, these will be rounded to
a supported vector length and returned from the prctl(). Add a test which
exercises this for every valid vector length and makes sure that the return
value is as expected and that this is reflected in the actual system state.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Link: https://lore.kernel.org/r/20210929151925.9601-5-broonie@kernel.org


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