mfd: cgbc: Add support for HWMON

The Board Controller has some internal sensors. Add a hwmon cell for the
cgbc-hwmon driver which adds support for temperature, voltage, current
and fan sensors.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://lore.kernel.org/r/20250203-congatec-board-controller-hwmon-v4-2-ff6c76a4662c@bootlin.com


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