drm: fix inclusion of drm.h in vmwgfx_drm.h

Using `#include "drm.h"` instead of `#include <drm/drm.h>` allow drm
headers to be moved in another directory without changes, like for the
libdrm imports.
Signed-off-by: Gabriel Laskar <gabriel@lse.epita.fr>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
CC: Emil Velikov <emil.l.velikov@gmail.com>
CC: Mikko Rapeli <mikko.rapeli@iki.fi>

include/uapi/drm/vmwgfx_drm.h

@@ -28,9 +28,7 @@
 #ifndef __VMWGFX_DRM_H__
 #define __VMWGFX_DRM_H__
 
-#ifndef __KERNEL__
-#include <drm/drm.h>
-#endif
+#include "drm.h"
 
 #define DRM_VMW_MAX_SURFACE_FACES 6
 #define DRM_VMW_MAX_MIP_LEVELS 24