gpio: samsung: skip gpio lib registration for EXYNOS5440

Since exynos5440 can support pinctrl so skip the legacy
gpiolib registration. If not, happens following.

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

Acked-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>