msm: mdss: synchronize wfd driver iommu mmap/munmap with mdss

Add clocks reference during wfd driver iommu mdp_mmap/mdp_munmap
to ensure iommu is in proper state while wfd driver map/un-map
any buffers.

Change-Id: Id1a24285b81d5047e5e9f002ade9694ea49be59d
Signed-off-by: Pawan Kumar <pavaku@codeaurora.org>