pinctrl: UniPhier: add UniPhier pinctrl core support

The core support for the pinctrl drivers for all the UniPhier SoCs.

Changes in v2:
  - drop vogus THIS_MODULE because this file is always built-in
  - drop vogus "include <linux/module.h> because this file is
    always built-in

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>