drm/omap: panel-tpo-td028ttec1: Drop unneeded linux/gpio.h header

The driver doesn't use GPIOs and thus doesn't need to include the
linux/gpio.h header.

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>