drm/omap: tpd12s015: CT_CP_HPD as optional gpio

tpd12s015 HW has LS_OE, CT_CP_HPD and HPD gpios. Out of these gpios,
driver only handled LS_OE as optional. The CT_CP_HPD gpio should also
be treated as optional gpio as it is just a power saving feature. Some
boards hardwire this gpio to be always enable. In this patch, all access
to CT_CP_HPD gpio is made optional.

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