pinctrl: exynos: change PINCTRL_EXYNOS option

Since pinctrl-exynos can support exynos4 and exynos5 so changed
the option name to PINCTRL_EXYNOS for more clarity.

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