regulator: dt-bindings: Clean-up active-semi,act8945a duplication

The active-semi,act8945a binding is documented in multiple places. The
charger child node is documented in regulator/active-semi,act8945a.yaml
and power/supply/active-semi,act8945a-charger.yaml. An old text binding
is in mfd/act8945a.txt.

Update the regulator/active-semi,act8945a.yaml with the additional
descriptions and constraints from
power/supply/active-semi,act8945a-charger.yaml, and then remove it and
mfd/act8945a.txt.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250807214459.4173892-1-robh@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>