kselftest/arm64: Limit the maximum VL we try to set via ptrace

When SVE was initially merged we chose to export the maximum VQ in the ABI
as being 512, rather more than the architecturally supported maximum of 16.
For the ptrace tests this results in us generating a lot of test cases and
hence log output which are redundant since a system couldn't possibly
support them. Instead only check values up to the current architectural
limit, plus one more so that we're covering the constraining of higher
vector lengths.

This makes no practical difference to our test coverage, speeds things up
on slower consoles and makes the output much more managable.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230111-arm64-kselftest-ptrace-max-vl-v1-1-8167f41d1ad8@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest/arm64: Add coverage for the ZA ptrace interface

Add some basic coverage for the ZA ptrace interface, including walking
through all the vector lengths supported in the system. Unlike SVE
doing syscalls does not discard the ZA state so when we set data in ZA
we run the child process briefly, having it add one to each byte in ZA
in order to validate that both the vector size and data are being read
and written as expected when the process runs.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419112247.711548-38-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>