ARM: h1940: Use gpiolib for latch access

This patch adds gpiolib support for h1940 latch.
With this patch it's possible to use leds-gpio and uda1380
drivers (they require gpiolib support for appropriate pins).
And now it's possible to drop leds-h1940 driver.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>