leds: Convert S3C24XX LED driver to gpiolib API

The s3c2410_gpio* calls are obsolete and have been scheduled for
removal since several kernel releases. Remove them and use common
gpiolib API instead.
This patch also adds gpio_request/gpio_free call for API corectness.

It is a prerequisite for removal of the S3C24XX SoC specific
arch/arm/plat-samsung/include/gpio-fns.h header.

Tested on Micro2440-SDK.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>