pinctrl: uniphier: set pinctrl_desc name in common probe function

Every SoC driver sets the same name for struct pinctrl_desc and
platform_driver.  The common probe function can set desc->name
instead of duplicating strings in each SoC driver.

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