drm: omapdrm: Move FEAT_HDMI_* features to hdmi4 driver

The FEAT_HDMI_* features are specific to the HDMI4, move them from the
omap_dss_features structure to the hdmi4 driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>