IIRC, MFD devices support binding subdevices to the OF nodes. Do you
plan to use it? Could you possibly point out the example DTs?

I'm not planning to add this, we want to move away from using the
cros_ec_dev mfd to load cros_ec_ucsi. On upcoming devices using
cros_ec_ucsi will just be loaded based on ACPI/DT. Regarding example
DTs, I'll point this out in the comment.