i2c bus via USB adapter

  Along with trying to attach some I2C devices to my RPI4 (which has
GPIO-pin exposure issues due to heatsink-case), I tried attaching this
device from Adafruit:

	Adafruit MCP2221A Breakout - General Purpose USB to GPIO ADC I2C Stemma QT / Qwiic
	https://www.adafruit.com/product/4471

  When I plug it into my box, I see this info:

	kernel: ugen0.4: <Microchip Technology Inc. MCP2221 USB-I2C/UART Combo> at usbus0
	kernel: umodem0 on uhub2
	kernel: umodem0: <Microchip Technology Inc. MCP2221 USB-I2C/UART Combo, class 239/2, rev 2.00/1.00, addr 3> on usbus0
	kernel: umodem0: data interface 1, has no CM over data, has no break
	kernel: uhid0 on uhub2
	kernel: uhid0: <Microchip Technology Inc. MCP2221 USB-I2C/UART Combo, class 239/2, rev 2.00/1.00, addr 3> on usbus0

  I've got a /dev/iic0, but that doesn't seem to be from this device:

	...
	iichb0: <BCM2708/2835 BSC controller> mem 0x7e804000-0x7e804fff irq 26 on simplebus0
	...
	kernel: iicbus0: <OFW I2C bus> on iichb0
	kernel: iic0: <I2C generic I/O> on iicbus0

  Simple recursive grepping didn't get me any hits for MCP2221, and there is
a TON of hits for Microchip, so currently assuming that FreeBSD doesn't have
a driver yet.  Total ignorance at this point, but if there was a driver, would
the expected behavior (assuming right drivers are loaded) would be for the
system to figure out there was an I2C bus hiding behind it and make another
/dev/iic# available, devoted to it?

  A ugen driver (generic USB) seems right.  The umodem driver seems
reasonable (serial device).  The uhid driver seems wrong, at least in
this case, but of course most of the hits I see on the forums are mice
and such, so maybe misidentified in this case.