ARM: S5PC100: Use common functions for gpiolib implementation

GPIOlib helpers from plat-samsung already have functions for accessing
4bit gpio banks. This patch removes the duplicated functions from
plat-s5pc1xx/gpiolib.c.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>