video/pxa: LCD_CORGI needs BACKLIGHT_CLASS_DEVICE

This fixes a randconfig build error when BACKLIGHT_CLASS_DEVICE
is disabled, by describing the dependency in Kconfig,
as we do for the other drivers in this directory.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>