ARM: dts: atlas7: add pinctrl and gpio descriptions

This patch adds pinctrl and gpio stuff according to the atlas7
pinctrl driver.

Signed-off-by: Wei Chen <Wei.Chen@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>