How do I use the SPI feature in a ME9210 Linux.

I presently disable serial in the kernel, load the gpio insmod and bit bang the GPIO pins. Surely the SPI FIM will do it better and faster - but where to find out how? Is this a custom ME9210?

you need to use spidev driver. Please check online documentation inside Digi ESP, search for SPI or spidev.
ME9210 has native interface so you do not have to use the FIM.

Is this also true for the i2c?