drm: move drm vblank initialization/cleanup to driver load/unload

drm vblank initialization keeps track of the changes in driver-supplied
frame counts across vt switch and mode setting, but only if you let it by
not tearing down the drm vblank structure.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -47,6 +47,8 @@ enum pipe {
 	PIPE_B,
 };
 
+#define I915_NUM_PIPE	2
+
 /* Interface history:
  *
  * 1.1: Original.