pinctrl: uniphier: guard uniphier directory with CONFIG_PINCTRL_UNIPHIER

CONFIG_PINCTRL_UNIPHIER is more suitable than CONFIG_ARCH_UNIPHIER
to guard the drivers/pinctrl/uniphier directory.

The current CONFIG_PINCTRL_UNIPHIER_CORE is a bit long
(it would break the indentation in drivers/pinctrl/Makefile),
so rename it into CONFIG_PINCTRL_UNIPHIER.

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