ARM: SAMSUNG: Introduce GPIO_SAMSUNG Kconfig entry

This patch adds Kconfig entry that selects whether legacy Samsung GPIO
driver should be built or not. For platforms that support only DT based
boot, the new pinctrl driver is used and so the old one is not needed.

Cc: Grant Likely <grant.likely@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>