gpu: nvgpu: update common.gr doxygen

Add below updates to common.gr doxygen:

- Add doxygen comments for APIs that are mentioned in RM SWAD and in
  RM-common.gr traceability document.
- Comment about valid ranges for input parameters of bunch of functions.
- Add nvgpu_assert() to ensure correct value is passed as input
  parameter to number of functions.
- Add references to relevant functions with @see.
- Update Targets field for unit tests to cover newly doxygenated
  functions.
- Update unit test test_gr_init_hal_pd_skip_table_gpc to take care of
  new asserts added into some APIs.

Jira NVGPU-6180

Change-Id: Ie889bed96b6428b1fd86dcf30b322944464e9d12
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2469397
(cherry picked from commit 5d7d7e9ce1c4efe836ab842d7962a3aee4e8972f)
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2469394
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-misra <svc-mobile-misra@nvidia.com>
Reviewed-by: svc-mobile-cert <svc-mobile-cert@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/gr/ctx.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2019-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -52,6 +52,7 @@ void nvgpu_gr_ctx_desc_free(struct gk20a *g,
 void nvgpu_gr_ctx_set_size(struct nvgpu_gr_ctx_desc *gr_ctx_desc,
 	u32 index, u32 size)
 {
+	nvgpu_assert(index < NVGPU_GR_CTX_COUNT);
 	gr_ctx_desc->size[index] = size;
 }