OMAPDSS: generic dpi panel: handle gpios in panel driver

The generic dpi 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.

Add a generic way of passing gpio information to the generic dpi panel driver
via it's platform_data. This information includes the number of gpios used by
the panel, the gpio number and logic level (active high/low) for each gpio. This
gpio data will be used by the driver to request and configure the gpios required
by the panel.

This will help in removing the need for the panel drivers to have platform
related callbacks.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Archit Taneja <archit@ti.com>