pinctrl: axp209: add support for AXP813 GPIOs

The AXP813 has only two GPIOs. GPIO0 can either be used as a GPIO, an
LDO regulator or an ADC. GPIO1 can be used either as a GPIO or an LDO
regulator.

Moreover, the status bit of the GPIOs when in input mode is not offset
by 4 unlike the AXP209.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>