mfd: axp20x: Enable AXP22X regulators

Now that the axp20x-regulators driver supports different variants of the
AXP family, we can enable regulator support for AXP22X without the risk
of incorrectly configuring regulators.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>