Revert "iommu/arm-smmu: Leave power resources enabled across unmap and sync ops"

This reverts commit fc6d479bac4c756359388647d45f39f08d0c8534. The
functionality offered by this change was not implemented correctly,
so revert it in favor of a different way of addressing the issue
that was supposed to be fixed.

Change-Id: Id061372026dea2960758c4dad0a5e37c2604576e
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>