gpio:samsung s5p_ suffix add for GPIO functions

This change is driven by need of general gpio_* functions,
which as their parameter are accepting the GPIO pin number, NOT
block and pin.

This makes the code alike to omap, and allows for using more
generic frameworks (e.g. software I2C).

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>