ARM: EXYNOS: Select PINCTRL_EXYNOS for exynos4/5 at chip level

Previously if you had MACH_EXYNOS5_DT but not MACH_EXYNOS4_DT you'd be
missing the pincontrol definitions.  Move PINCTRL selects to the arch
level since we should be enabling the code for all exynos variants.

Update the PINCTRL descriptions to indicate that PINCTRL_EXYNOS is not
for exynos5440.  Also add basic dependencies for the PINCTRL_EXYNOS
kernel config.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>