gpio: samsung: refactor gpiolib init for exynos4/5

Only code move, no functional change.

Main reason to do this was to get rid of the warnings:

drivers/gpio/gpio-samsung.c: In function 'samsung_gpiolib_init':
drivers/gpio/gpio-samsung.c:2974:1: warning: label 'err_ioremap4' defined but not used [-Wunused-label]
drivers/gpio/gpio-samsung.c:2722:47: warning: unused variable 'gpio_base4' [-Wunused-variable]

without adding more ifdef mess.

I think this whole file would do well being coverted over to a platform
driver and moving most of the tables out to SoC code and/or device trees,
but since that changes init ordering it needs to be done with some care,
i.e. not at this time.

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>