mfd: axp20x: Add support for 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
converter, which adds another register.

Add the required boilerplate to introduce a new PMIC to the AXP MFD
driver. Where possible, this just maps into the existing structs defined
for the AXP313A, only deviating where needed.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20241007001408.27249-5-andre.przywara@arm.com


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