OMAPDSS: HDMI: Move GPIO handling to HDMI driver

We currently manage HDMI GPIOs in the board files via
platform_enable/disable calls. This won't work with device tree, and in
any case the correct place to manage the GPIOs is in the HDMI driver.

This patch moves the handling of the GPIOs to the HDMI driver. The GPIO
handling is moved to the common hdmi.c file, and this probably needs to
be revisited when adding OMAP5 HDMI support to see if the GPIO handling
needs to be moved to IP specific files.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>