Add support for the ICM 20948 IMU

[ShadedSelf]

Most MPU 9xxx/6xxx seem to be clones and not very good quality since the original ones are no longer manufactured.
This PR adds support for the ICM 20948 IMU, the succesor to the MPU 9xxx.

[greymfm]

Nice! There are quite a few Arduino's around (Arduino Due/Adafruit M4) running the Sunray code. These micros probably don't have enough speed to run the IMU pipeline with 20 Hz. Just for supporting the ICM IMU, increasing the IMU FIFO frequency does not seem to be necessary? :-)

[ShadedSelf]

I set it to 20hz to match #145, probably not necessary in most cases yeah, the idea was to improve accuracy as much as possible when GPS is not available, also motor logic runs at 20hz in sunray IIRC.

Works OK on the M4, not sure about the Due.

Ive added a define to the settings now, it defaults to 5hz.