kselftest/arm64: abi: fix SVCR detection

kselftest/arm64: abi: fix SVCR detection

When using svcr_in to check ZA and Streaming Mode, we should make sure
that the value in x2 is correct, otherwise it may trigger an Illegal
instruction if FEAT_SVE and !FEAT_SME.

Fixes: 43e3f85523e4 ("kselftest/arm64: Add SME support to syscall ABI test")
Signed-off-by: Weizhao Ouyang <o451686892@gmail.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241211111639.12344-1-o451686892@gmail.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>