gpu: nvgpu: Do not touch gr status mask

gpu: nvgpu: Do not touch gr status mask

GR status disable mask was never set, so driver always disabled all
engines from status rollup.

Bug 1550628

Change-Id: I500a127be9253294f73d1f42ce89b886471a9117
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/719141
(cherry picked from commit 34a5ffe7e7dcc4df5f3a11848b828e96c43d2c4d)
Reviewed-on: http://git-master/r/719881
(cherry picked from commit 05181f92386ed7ee0c37baec333361890bb3daec)
Reviewed-on: http://git-master/r/727060
Reviewed-by: Mitch Luban <mluban@nvidia.com>