KVM: arm64: Pass level hint to TLBI during stage-2 permission fault

Alex pointed out that we don't pass a level hint to the TLBI instruction
when handling a stage-2 permission fault, even though the walker does
at some point have the level information in its hands.

Rework stage2_update_leaf_attrs() so that it can optionally return the
level of the updated pte to its caller, which can in turn be used to
provide the correct TLBI level hint.

Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/595cc73e-636e-8b3a-f93a-b4e9fb218db8@arm.com
Link: https://lore.kernel.org/r/20200930131801.16889-1-will@kernel.org