pinctrl: sunxi: Add Allwinner A20 pins set

The Allwinner A20 is pin-compatible with the older A10, so the two pin
set are quite similar. However, since the A20 has new features, we can't
just use the A10 pin set as is, and we need to define our own for the
A20.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>