drm/omap: displays: connector-hdmi: Support for hot plug detection

If the hpd_gpio is valid, use interrupt handler to react to HPD changes.
In case the hpd_gpio is not valid, try to enable hpd detection on the
encoder if it supports it.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>