gpio/exynos4: Fix incorrect mapping of gpio pull-up macro to register setting

The S3C_GPIO_PULL_UP macro value incorrectly maps to a reserved setting of GPIO
pull up/down registers on Exynos4 platform. Fix this incorrect mapping by adding
wrappers to the s3c_gpio_setpull_updown and s3c_gpio_getpull_updown functions.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>