kselftest/arm64: Fix syscall-abi for systems without 128 bit SME

kselftest/arm64: Fix syscall-abi for systems without 128 bit SME

[ Upstream commit 8ee0ac3bd6896878fe9fd867f1f7779062a13a0a ]

SME does not mandate any specific VL so we may not have 128 bit SME but
the algorithm used for enumerating VLs assumes that we will. Add the
required check to ensure that the algorithm terminates.

Fixes: 2063759f548e ("kselftest/arm64: Add SME support to syscall ABI test")
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221223-arm64-syscall-abi-sme-only-v1-1-4fabfbd62087@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>