radeon: add support for vblank on crtc2

This adds support for CRTC2 vblank on radeon similiar to the i915.

Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/char/drm/radeon_cp.c b/drivers/char/drm/radeon_cp.c
index aac5db3..7dd9800 100644
--- a/drivers/char/drm/radeon_cp.c
+++ b/drivers/char/drm/radeon_cp.c
@@ -1420,6 +1420,10 @@
 		return DRM_ERR(EINVAL);
 	}
 
+	/* Enable vblank on CRTC1 for older X servers
+	 */
+	dev_priv->vblank_crtc = DRM_RADEON_VBLANK_CRTC1;
+
 	switch(init->func) {
 	case RADEON_INIT_R200_CP:
 		dev_priv->microcode_version = UCODE_R200;