vmwgfx: Add vblank stubs

This fixes kernel panics when running the vbltest from the drm repo. We
can't just skip initializing the vblank system since it sets up certain
state for us, see: "vmwgfx: Enable use of the vblank system."

Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
index 0e9b2ce..30589d0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
@@ -618,6 +618,8 @@
 				uint32_t pitch,
 				uint32_t height);
 u32 vmw_get_vblank_counter(struct drm_device *dev, int crtc);
+int vmw_enable_vblank(struct drm_device *dev, int crtc);
+void vmw_disable_vblank(struct drm_device *dev, int crtc);
 int vmw_kms_present(struct vmw_private *dev_priv,
 		    struct drm_file *file_priv,
 		    struct vmw_framebuffer *vfb,