As A20 is designed as a pin-compatible upgrade of A10, their pin
controller are very similar, and can share one driver.

Add A20 support to the A10 driver.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>