via_drm.h: move struct via_file_private definition to drivers/gpu/drm/via/via_drv.h

Fixes userspace compile error since list_head is not exported to userspace
headers.

Suggested by Emil Velikov <[e-mail]> at
https://lkml.org/lkml/2015/6/3/792

Signed-off-by: Mikko Rapeli <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/via/via_drv.h

···
 	uint32_t dma_diff;
 } drm_via_private_t;
 
+struct via_file_private {
+	struct list_head obj_list;
+};
+
 enum via_family {
   VIA_OTHER = 0,     /* Baseline */
   VIA_PRO_GROUP_A,   /* Another video engine and DMA commands */

include/uapi/drm/via_drm.h

···
 	drm_via_blitsync_t sync;
 } drm_via_dmablit_t;
 
-struct via_file_private {
-	struct list_head obj_list;
-};
-
 #endif				/* _VIA_DRM_H_ */