Hi Adam. I just so happen to be adding support for the Adafruit
ItsyBitsy M4 board ATM. It's SAMD51 based which seems to be basically
the same as the SAMG55.

I've checked the UART, GPIO, SPI, and watchdog drivers so far. I'm
adding a PWM and QSPI driver, and will check the USB driver.

You'll need to create your own board definition and to create the
device tree files.

-- Michael