arm64/sme: Don't use streaming mode to probe the maximum SME VL

arm64/sme: Don't use streaming mode to probe the maximum SME VL

During development the architecture added the RDSVL instruction which means
we do not need to enter streaming mode to enumerate the SME VLs, use it
when we probe the maximum supported VL. Other users were already updated.

No functional change.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221223-arm64-sme-probe-max-v1-1-cbde68f67ad0@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>