gpio: exynos4: skip gpiolib registration if pinctrl driver is used

Pinctrl driver, when enabled, registers all the gpio pins and hence the
registration of gpio pins by this driver can be skipped.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>