kselftest/arm64: Validate SVCR in streaming SVE stress test

kselftest/arm64: Validate SVCR in streaming SVE stress test

In the ZA and ZT test programs we explicitly validate that PSTATE.ZA is as
expected on each loop but we do not do the equivalent for our streaming
SVE test, add a check that we are still in streaming mode on every loop
in case that goes wrong.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230922-arm64-ssve-validate-svcr-v1-1-f518960eaeda@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>