regulator: axp20x: support AXP809 variant

The X-Powers AXP809 PMIC has a similar set of regulators as the AXP221,
though a few LDOs were removed, and a new switch output added. Like the
AXP221, AXP809 also has DC1SW and DC5LDO, which are internally chained
to DCDC1 and DCDC5, respectively.

Add support for this new variant. Also remove the "axp22x_" prefix from
DC1SW/DC5LDO supply handling code, as the AXP809 uses it as well.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>