gpio/samsung: add support GPIOlib for EXYNOS5250

This patch adds gpio_chips for EXYNOS5250 and replaces
exynos4_xxx() with exynos_xxx() and variables to support
exynos4 and exynos5 together.
In addition, use ioreamp() for base address of gpios.

Signed-off-by: Sangsu Park <sangsu4u.park@samsung.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>