ARM: EXYNOS: enable PINCTRL for EXYNOS5440

This patch removes following warning in kernel boot log,
Because EXYNOS5440 can support only Pinctrl not GPIO.

WARNING: at drivers/gpio/gpio-samsung.c:3102 samsung_gpiolib_init+0x68/0x8c()
Unknown SoC in gpio-samsung, no GPIOs added

Cc: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>