Some headers specify that files are under dual-licensed GPL2.0+
and X11. But in fact, it turns out that the full licenses texts
associated are GPL2.0+ and MIT.

Fix license headers to reflect real licenses associated.
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>