ARM: S5P64X0: Change GPIOlib initialization to core_initcall

This patch changes the gpiolib initialization from arch_initcall
to core_initcall will allow us to make use of gpio functions in
smdk64x0_machine_init function.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>