regulator: s2mps11: add S2MPG11 regulator

The S2MPG11 PMIC is a Power Management IC for mobile applications with
buck converters, various LDOs, power meters, and additional GPIO
interfaces. It typically complements an S2MPG10 PMIC in a main/sub
configuration as the sub-PMIC.

It has 12 buck, 1 buck-boost, and 15 LDO rails. Several of these can
either be controlled via software (register writes) or via external
signals, in particular by:
    * input pins connected to a main processor's:
        * GPIO pins
        * other pins that are e.g. firmware- or power-domain-controlled
          without explicit driver intervention
    * a combination of input pins and register writes.

Control via input pins allows PMIC rails to be controlled by firmware,
e.g. during standby/suspend or as part of power domain handling where
otherwise that would not be possible. Additionally toggling a pin is
faster than register writes, and it also allows the PMIC to ensure that
any necessary timing requirements between rails are respected
automatically if multiple rails are to be enabled or disabled quasi
simultaneously.

This commit implements support for all these rails and control
combination.

Note1: For an externally controlled rail, the regulator_ops provide an
empty ::enable() and no ::disable() implementations, even though Linux
can not enable the rail and one might think ::enable could be NULL.
Without ops->enable(), the regulator core will assume enabling such a
rail failed, though, and in turn never add a reference to its parent
(supplier) rail. Once a different (Linux-controlled) sibling (consumer)
rail on that same parent rail gets disabled, the parent gets disabled
(cutting power to the externally controlled rail although it should
stay on), and the system will misbehave.

Note2:  While external control via input pins appears to exist on other
versions of this PMIC, there is more flexibility in this version, in
particular there is a selection of input pins to choose from for each
rail (which must therefore be configured accordingly if in use),
whereas other versions don't have this flexibility.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://patch.msgid.link/20260122-s2mpg1x-regulators-v7-19-3b1f9831fffd@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

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