pinctrl: sunxi: Fix recursive dependency

Fix the following configuration error:
drivers/pinctrl/sunxi/Kconfig:3:error: recursive dependency detected!
drivers/pinctrl/sunxi/Kconfig:3:	symbol PINCTRL_SUNXI is selected by PINCTRL_SUN4I_A10
drivers/pinctrl/sunxi/Kconfig:9:	symbol PINCTRL_SUN4I_A10 default value contains PINCTRL_SUNXI

Add a new intermedia PINCTRL_SUNXI_COMMON, that superseeds the PINCTRL_SUNXI
one.

We still need to keep PINCTRL_SUNXI at the moment in order to preserve
bisectability. Indeed, during that merge window, we also introduced the
MACH_SUN* symbols. Since it's going through different trees, we can't rely on
the fact that the options will be there, while ARCH_SUNXI still select
PINCTRL_SUNXI.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>