power: supply: add support for S2MU005 battery fuel gauge device

power: supply: add support for S2MU005 battery fuel gauge device

Samsung's S2MU005 PMIC, which contains battery charger functionality
also includes a battery fuel gauge device, which is separate from the
PMIC itself, and typically connected to an I2C bus. Add a generic driver
to support said device.

Signed-off-by: Yassine Oudjana <y.oudjana@protonmail.com>
Co-developed-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Link: https://patch.msgid.link/20260304-s2mu005-fuelgauge-v3-2-e4dc4e47cde8@disroot.org
[Moved mutex init before power-supply registration]
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>