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, so rename it
into CONFIG_PINCTRL_UNIPHIER.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>