ARM: dts: omap4: enable CEC pin for Pandaboard A4 and ES

The CEC pin was always pulled up, making it impossible to use it.

Change to PIN_INPUT so it can be used by the new CEC support.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>