ARM: S5P64X0: remove gpiolib.c file in mach-s5p64x0

Since S5P64X0 gpiolib is supported in drivers/gpio/gpio-samsung.c,
this can be removed. Probably, removing this file is missed when
S5P64X0 gpiolib was supported in drivers/gpio/.
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>