arm64: Filter out SME hwcaps when FEAT_SME isn't implemented

We have a number of hwcaps for various SME subfeatures enumerated via
ID_AA64SMFR0_EL1. Currently we advertise these without cross checking
against the main SME feature, advertised in ID_AA64PFR1_EL1.SME which
means that if the two are out of sync userspace can see a confusing
situation where SME subfeatures are advertised without the base SME
hwcap. This can be readily triggered by using the arm64.nosme override
which only masks out ID_AA64PFR1_EL1.SME, and there have also been
reports of VMMs which do the same thing.

Fix this as we did previously for SVE in 064737920bdb ("arm64: Filter
out SVE hwcaps when FEAT_SVE isn't implemented") by filtering out the
SME subfeature hwcaps when FEAT_SME is not present.

Fixes: 5e64b862c482 ("arm64/sme: Basic enumeration support")
Reported-by: Yury Khrustalev <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

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