arm: omap: dss-common: use picodlp panel's gpio handling

The dss-common file currently requests gpios required by the picodlp DPI
panel on the 4430sdp/blaze board. It also requests DISPLAY_SEL_GPIO and
DLP_POWER_ON_GPIO gpios which are board specific gpios to switch between lcd2
panel and picodlp, and setting intermediate power supplies for picodlp
respectively. These gpios are toggled through platform_enable/disable functions
called by the picodlp driver.

Remove the gpio requests for the gpios which are already requested by the panel
driver, and remove the platform callback functions and set the platform specific
gpios in such a way that lcd2 panel is selected for the LCD2 overlay manager and
the power supplies for picodlp are disabled.

Note: We need to revisit this so that we can enable and switch to picodlp if
that's the only panel driver available for the LCD2 overlay manager.

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