drm: drm_mode.h fix includes

Instead of using linux/types.h, drm headers should use drm.h, in order
to handle the portability issues in only one place.

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>