gpu: nvgpu: gr_priv header include cleanup

Add more apis in gr_utils for accessing variables within gr struct.
This helps to avoid including gr_priv.h outside gr files and
derefencing gr struct.

Jira NVGPU-3218

Change-Id: I6f24cc302f10aa1da14a981d80c400a027c9a115
Signed-off-by: Vinod G <vinodg@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2115930
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

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

@@ -28,6 +28,7 @@
 #include <nvgpu/gk20a.h>
 #include <nvgpu/gr/config.h>
 #include <nvgpu/gr/gr.h>
+#include <nvgpu/gr/gr_utils.h>
 #include <nvgpu/channel.h>
 #include <nvgpu/tsg.h>
 #include <nvgpu/fifo.h>