arm64: Add the arm64.nosme command line option

In order to be able to completely disable SME even if the HW
seems to support it (most likely because the FW is broken),
move the SME setup into the EL2 finalisation block, and
use a new idreg override to deal with it.

Note that we also nuke id_aa64smfr0_el1 as a byproduct.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220630160500.1536744-8-maz@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>