KVM: arm64: pkvm: Use the mm_ops indirection for cache maintenance

CMOs issued from EL2 cannot directly use the kernel helpers,
as EL2 doesn't have a mapping of the guest pages. Oops.

Instead, use the mm_ops indirection to use helpers that will
perform a mapping at EL2 and allow the CMO to be effective.

Fixes: 25aa2869 ("KVM: arm64: Move guest CMOs to the fault handlers")
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220114125038.1336965-1-maz@kernel.org