arm: omap: board-devkit8000: use generic dpi panel's gpio handling

The devkit8000 board file currently requests gpios required to configure the
innolux DPI panel, and provides platform_enable/disable callbacks to configure
them.

These tasks have been moved to the generic dpi panel driver itself and should
be removed from the board files.

Remove the gpio request and the platform callbacks from the board file.
Configure the gpio information in generic dpi panel's platform data so that it's
passed to the panel driver.

Signed-off-by: Archit Taneja <archit@ti.com>
Cc: Tony Lindgren <tony@atomide.com>