HACK: drm/msm/mdp5: Enable runtime pm before attaching iommu

The arm-smmu driver used by MSM8996 implements runtime PM using
device links. This requires the consumer device (i.e. MDP) to call
pm_runtime_get_sync() before using the iommu.

MDP driver does that later, causing the driver to crash when try
to attach the iommu. Move the pm_runtime_get_sync() call earlier.
Also, move the put_sync() call in kms_destroy for now, since that
disabling it any earlier would disable the arm-smmu. This will be
removed once the MDP driver is runtime PM adapted.

Signed-off-by: Archit Taneja <architt@codeaurora.org>