pinctrl: sunxi: Replace hardcoded pin defines by a macro

We previously had an evergrowing (and exhaustive) list of the pins that could
be used on any Allwinner SoCs. These defines were then used by each pinctrl
driver to declare the list of functions for this pin. Since it's pretty much
all boilerplate, we can remove it just by a single macro.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>