drm/amdgpu: protect fence_process from multiple context

fence_process may be called from kthread, user thread and interrupt context.
it is possible to called concurrently, then will wake up fence queue multiple times.

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -869,6 +869,7 @@ struct amdgpu_ring {
 	struct amdgpu_fence_driver	fence_drv;
 	struct amd_gpu_scheduler 	*scheduler;
 
+	spinlock_t              fence_lock;
 	struct mutex		*ring_lock;
 	struct amdgpu_bo	*ring_obj;
 	volatile uint32_t	*ring;