gpu: nvgpu: fix runlist update timeout handling

bug 1625901
1) disable ELPG before doing GR reset when runlist update times out
2) add mutex for GR reset to avoid multiple threads resetting GR
3) protect GR reset with FECS mutex so that no one else submits methods

Change-Id: I02993fd1eabe6875ab1c58a40a06e6c79fcdeeae
Signed-off-by: Vijayakumar <vsubbu@nvidia.com>
Reviewed-on: http://git-master/r/793643
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

drivers/gpu/nvgpu/gk20a/fifo_gk20a.h

@@ -109,6 +109,7 @@ struct fifo_gk20a {
 	/* zero-kref'd channels here */
 	struct list_head free_chs;
 	struct mutex free_chs_mutex;
+	struct mutex gr_reset_mutex;
 
 	struct tsg_gk20a *tsg;
 	struct mutex tsg_inuse_mutex;