arm64/sysreg: Describe ID_AA64SMFR0_EL1.SMEVer as an enumeration

arm64/sysreg: Describe ID_AA64SMFR0_EL1.SMEVer as an enumeration

As with the corresponding SVE field ID_AA64ZFR0_EL1.SVEVer and other ID
register fields the SMEVer field should be identified as an enumeration
but it is currently described as a plain field (most likely due to there
presently being only one possible value). Update it to be an enumeration
as one would expect. No functional change.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Kristina Martsenko <kristina.martsenko@arm.com>
Link: https://lore.kernel.org/r/20220905225425.1871461-3-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>