drm/omap: panel-sony-acx565akm: Convert to the GPIO descriptors API

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>