Add i915 ioctls to configure pipes for vblank interrupt.

i915 vblanks can be generated from either pipe a or b, however a disabled
pipe generates no interrupts. This change allows the X server to select
which pipe generates vblank interrupts.

From: Keith Packard <keith.packard@intel.com> via DRM CVS
Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/char/drm/i915_dma.c b/drivers/char/drm/i915_dma.c
index 9f4b8ce..a94233b 100644
--- a/drivers/char/drm/i915_dma.c
+++ b/drivers/char/drm/i915_dma.c
@@ -758,7 +758,9 @@
 	[DRM_IOCTL_NR(DRM_I915_FREE)] = {i915_mem_free, DRM_AUTH},
 	[DRM_IOCTL_NR(DRM_I915_INIT_HEAP)] = {i915_mem_init_heap, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY},
 	[DRM_IOCTL_NR(DRM_I915_CMDBUFFER)] = {i915_cmdbuffer, DRM_AUTH},
-	[DRM_IOCTL_NR(DRM_I915_DESTROY_HEAP)] = { i915_mem_destroy_heap, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY }
+	[DRM_IOCTL_NR(DRM_I915_DESTROY_HEAP)] = { i915_mem_destroy_heap, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY },
+	[DRM_IOCTL_NR(DRM_I915_SET_VBLANK_PIPE)] = { i915_vblank_pipe_set, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY },
+	[DRM_IOCTL_NR(DRM_I915_GET_VBLANK_PIPE)] = { i915_vblank_pipe_get, DRM_AUTH },
 };
 
 int i915_max_ioctl = DRM_ARRAY_SIZE(i915_ioctls);