regulator: add support for SGM3804 Dual Output driver

Neil Armstrong <neil.armstrong@linaro.org> says:

Add support for the SG Micro SGM3804 Single Inductor Dual Output
Buck/Boost Converter used to power LCD panels a provide positive
and negative power rails with configurable voltage and active
discharge function for each output.

The SGM3804 is powered by the enable GPIO pins inputs and only
supports I2C write messages.
In order to add flexibility and simplify the driver, the
regmap cache is enabled and populated with default values
since we can't write registers when the 2 GPIOs are down.

This regulator is used to provide vsn and vsn power to the
Ayaneo Pocket S2 dual-DSI LCD panel.

Link: https://patch.msgid.link/20260522-topic-sm8650-ayaneo-pocket-s2-sgm3804-v5-0-bd6b1c300ecc@linaro.org

diff --cc drivers/regulator/qcom-rpmh-regulator.c
Simple merge