MAINTAINERS: Add Samsung pinctrl entries

It's convenient if get_maintainer suggests sending samsung/exynos
pinctrl changes to linux-samsung-soc and to Tomasz and Thomas.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>