iommu/arm-smmu: Add pm_runtime/sleep ops

The smmu needs to be functional only when the respective
master's using it are active. The device_link feature
helps to track such functional dependencies, so that the
iommu gets powered when the master device enables itself
using pm_runtime. So by adapting the smmu driver for
runtime pm, above said dependency can be addressed.

This patch adds the pm runtime/sleep callbacks to the
driver and also the functions to parse the smmu clocks
from DT and enable them in resume/suspend.

Also, while we enable the runtime pm add a pm sleep suspend
callback that pushes devices to low power state by turning
the clocks off in a system sleep.
Also add corresponding clock enable path in resume callback.

Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
[vivek: rework for clock and pm ops]
Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>