regulator: axp20x: add support for the AXP323

The X-Powers AXP323 is a very close sibling of the AXP313A. The only
difference seems to be the ability to dual-phase the first two DC/DC
converters.

Place the new AXP323 ID next to the existing AXP313A checks, to let
them share most code.
The only difference is the poly-phase detection code, which gets
extended to check the respective bit in a newly used register.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241007001408.27249-6-andre.przywara@arm.com


Signed-off-by: Lee Jones <lee@kernel.org>