video: tegra: host: use dma APIs in pmu_gk20a.c

video: tegra: host: use dma APIs in pmu_gk20a.c

- use dma_alloc_coherent()/dma_free_coherent() to
  allocate/free memory
- use gk20a_gmmu_map()/unmap() to update gmmu ptes

Bug 1397647

Change-Id: I7490ee0dbccd5461ab2b8993b557e40f9c20ff4a
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/337289
Reviewed-by: Sachin Nikam <snikam@nvidia.com>