drm: remove the dma_ioctl special-case

We might as well have a real ioctl function which checks for the
callbacks. This seems to be a remnant from back in the days when each
drm driver had their own complete ioctl table, with no shared core
drm table at all.

To make really sure no mis-guided user in a kms driver pops up again
explicitly check for that in the new ioctl implementation.

v2: Drop the unused variable I've accidentally left in the code,
spotted by David Herrmann.

Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 139d859..808eb23 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1355,6 +1355,8 @@
 			struct drm_file *file_priv);
 extern int drm_mapbufs(struct drm_device *dev, void *data,
 		       struct drm_file *file_priv);
+extern int drm_dma_ioctl(struct drm_device *dev, void *data,
+			 struct drm_file *file_priv);
 
 				/* DMA support (drm_dma.h) */
 extern int drm_legacy_dma_setup(struct drm_device *dev);