imx: ventana: export backlight gpio after gpio driver is available

imx: ventana: export backlight gpio after gpio driver is available

Calling request_gpio to register bklt_gpio with the GPIO driver had no effect
in setup_display called from early board init (although pinmuxing it and
configuring it as output-low does do what it should). Therefore move the
request_gpio later in enable_lvds so that its registered for use by the
gpio command if LVDS is actually enabled.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>