KVM: arm64: Add fast path to handle permission relaxation during dirty logging

To reduce MMU lock contention during dirty logging, all permission
relaxation operations would be performed under read lock.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220118015703.3630552-3-jingzhangos@google.com