vmwgfx: Enable use of the vblank system

This is to avoid accessing uninitialized data during
drm_irq_uninstall and vblank ioctls. At the same time, enable error check from
drm_kms_init which previously appeared to ignore all errors.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

@@ -518,6 +518,7 @@ void vmw_kms_write_svga(struct vmw_private *vmw_priv,
 			unsigned bbp, unsigned depth);
 int vmw_kms_update_layout_ioctl(struct drm_device *dev, void *data,
 				struct drm_file *file_priv);
+u32 vmw_get_vblank_counter(struct drm_device *dev, int crtc);
 
 /**
  * Overlay control - vmwgfx_overlay.c