s5p: gpio: change gpio coding method for s5p gpio.

Old s5p gpio coding method was not clean and was not working properly
for all parts and banks. New method is clean and easy to extend.

Gpio coding mask:
0x000000ff - pin number
0x00ffff00 - bank offset
0xff000000 - part number

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>