gpu: nvgpu: unit: add negative tests for common.gr.obj_ctx

Add negative tests that inject memory allocation failures and
HAL function call errors to verify error handling path in
common.gr.obj_ctx unit.

Update common.gr.setup test to cover invalid class input while
setting preemption mode.

Jira NVGPU-4457

Change-Id: I74d1ba63ba8aace6087b51fd50e2c136822d3a00
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2260939
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

userspace/SWUTS.h

@@ -108,6 +108,7 @@
  *   - @ref SWUTS-gr-fs-state
  *   - @ref SWUTS-gr-global-ctx
  *   - @ref SWUTS-gr-ctx
+ *   - @ref SWUTS-gr-obj-ctx
  *   - @ref SWUTS-gr-config
  *
  */