pinctrl: sunxi: guard sub-directory with CONFIG_PINCTRL_SUNXI

CONFIG_PINCTRL_SUNXI is more suitable than CONFIG_ARCH_SUNXI
to guard the drivers/pinctrl/sunxi/ directory.
(I renamed CONFIG_PINCTRL_SUNXI_COMMON to CONFIG_PINCTRL_SUNXI.)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>