iommu: arm-smmu: Restore iommu context in case of hibernation

During hibernation iommu-context registers are not retained,
so add a check and restore iommu registers if hibernation is
enabled.

Change-Id: Idc8f45b25aa6ff92602385c57ee1f2239a353418
Signed-off-by: Vivek Kumar <vivekuma@codeaurora.org>