regulator: axp20x: Add support for AXP22X regulators

Add AXP22X regulator definitions and variant id associations.
This introduces a new "switch" type output for one of the regulators.
It is a switchable secondary output of one regulator, with the same
voltage level as the primary output.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
[wens@csie.org: Moved variant choosing to multi family support patch]
[wens@csie.org: Add dc-dc work frequency range]
[wens@csie.org: Add "switch" type output regulator DC1SW]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>