gpu: nvgpu: MIG attributes enhancement

This CL covers the following code changes,
1) Added some more documentation for gpu_instance_id
   and gr_instance_id.
2) Used the gr_sys_pipe_id for gr_instance_id.
2) Removed gr_syspipe_id attribute.
4) Removed NVGPU_GPU_FLAGS_SUPPORT_MIG flag.
3) Changed the device node name to use gpu instance id + syspipe id
   combination insted of gpu instance id + gr engine instance id.

Bug 2802347

Change-Id: Id6ca7db5765ab31b5d83472be35dde432c2281ed
Signed-off-by: Lakshmanan M <lm@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2440532
Reviewed-by: automaticguardword <automaticguardword@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Rajesh Devaraj <rdevaraj@nvidia.com>
Reviewed-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit

drivers/gpu/nvgpu/os/linux/ioctl.c

@@ -386,7 +386,7 @@ static const struct nvgpu_mig_static_info nvgpu_default_pci_mig_static_info[] =
 	{
 		.instance_type = NVGPU_MIG_TYPE_MIG,
 		.major_instance_id = 2,
-		.minor_instance_id = 0,
+		.minor_instance_id = 4,
 	},
 };