pinctrl: sunxi: Support the 2.5V I/O bias mode

H616 and newer SoCs feature a 2.5V I/O bias mode in addition to the
1.8V and 3.3V modes. This mode is entered by selecting the 3.3V level
and disabling the "withstand function".

H616 supports this capability on its main PIO only. A100 supports this
capability on both its PIO and R-PIO.

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20220713025233.27248-4-samuel@sholland.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>