video: tegra: host: add separate functions to update gmmu ptes

video: tegra: host: add separate functions to update gmmu ptes

- existing function gk20a_vm_map() maps both user space and
  in-kernel buffers
- it has a lot of checking for user space buffers which is not
  required for in-kernel buffers
- add separate functions gk20a_gmmu_map()/unmap() to update
  gmmu ptes for in-kernel buffers only

Bug 1397647

Change-Id: I08f275203827c0e20deb9d6ab00c6e38fc094b12
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/333919
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>