kselftest/arm64: Add a stress test program for ZT0

Following the pattern for the other register sets add a stress test program
for ZT0 which continually loads and verifies patterns in the register in
an effort to discover context switching problems.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-14-f2fa0aef982f@kernel.org


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