pinctrl: sunxi: Add P2WI and RSB pinmuxes

P2WI and RSB are used to communicate with a PMIC. Most SoCs have only
one possible pinmux. F1C100s has two possibilities, with different mux
values, so omit it until some board needs one of them.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>