drm/amdgpu: add ctx_id to the WAIT_CS IOCTL (v4)

It is required to support fence per context.

v2: add amdgpu_ctx_get/put
v3: improve get/put
v4: squash hlock fix

Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
index 77bc574..ca0ea1e 100644
--- a/include/uapi/drm/amdgpu_drm.h
+++ b/include/uapi/drm/amdgpu_drm.h
@@ -260,7 +260,7 @@
 	uint32_t ip_type;
 	uint32_t ip_instance;
 	uint32_t ring;
-	uint32_t _pad;
+	uint32_t ctx_id;
 };
 
 struct drm_amdgpu_wait_cs_out {