OMAPDSS: n8x0 panel: handle gpio data in panel driver

The n8x0 panel driver leaves gpio configurations to the platform_enable and
disable calls in the platform's board file. These should happen in the panel
driver itself.

A platform data struct called panel_n8x0_data already exists to hold gpio
numbers and other platform data. However, the gpio requests are expected to be
done in the board file and not the panel driver.

Request all the gpios in the panel driver so that the board files which use
the the panel don't need to do it. This will help in removing the need for the
panel drivers to have platform related callbacks.

Signed-off-by: Archit Taneja <archit@ti.com>