video: hdmi: Relicense under MIT

In order to make it easier to port the code to other operating systems
(like the BSDs), relicense the HDMI helpers under the more permissive
MIT license.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>