gma500: Add the Oaktrail HDMI support

This differs enough from the Cedarview HDMI sufficiently to want to keep
them separated.

We need to sort out the power management for Oaktrail/Moorestown in order
to plumb this lot into the register handling logic.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>