drm: omapdrm: Keep vblank interrupt enabled while CRTC is active

Instead of going through a complicated private IRQ registration
mechanism, handle the vblank interrupt activation with the standard
drm_crtc_vblank_get() and drm_crtc_vblank_put() mechanism. This will let
the DRM core keep the vblank interrupt enabled as long as needed to
update the frame counter.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/gpu/drm/omapdrm/omap_irq.c b/drivers/gpu/drm/omapdrm/omap_irq.c
index e1925fa..1c82690 100644
--- a/drivers/gpu/drm/omapdrm/omap_irq.c
+++ b/drivers/gpu/drm/omapdrm/omap_irq.c
@@ -245,8 +245,10 @@ static irqreturn_t omap_irq_handler(int irq, void *arg)
 		struct drm_crtc *crtc = priv->crtcs[id];
 		enum omap_channel channel = omap_crtc_channel(crtc);
 
-		if (irqstatus & pipe2vbl(crtc))
+		if (irqstatus & pipe2vbl(crtc)) {
 			drm_handle_vblank(dev, id);
+			omap_crtc_vblank_irq(crtc);
+		}
 
 		if (irqstatus & dispc_mgr_get_sync_lost_irq(channel))
 			omap_crtc_error_irq(crtc, irqstatus);