drm/omap: remove unneeded gpio includes

encoder-opa362.c and panel-sharp-ls037v7dw01.c do not use the legacy
GPIO API, so we can remove the including of gpio.h and of_gpio.h.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>