video: tegra: host: gk20a: Use dmabuf directly

video: tegra: host: gk20a: Use dmabuf directly

Currently, gk20a memory management operations go through
nvhost_memmgr abstraction. This patch modifies gk20a driver
to use dmabuf API directly. At the same time this patch removes
unnecessary calls to take a reference on the memory manager itself.

In addition, this patch reworks the memmgr allocation not to take
memmgr as a parameter.

Bug 1450489

Change-Id: If46b7442f2d03c41b90a0e81f697f4ceb63c3dae
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/368447
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>