Adis16448 refactor

[mcsauder]

Hi,

This PR is the start of a larger effort to unify/standardize IMU driver implementations. Once all of the IMU drivers are structured/organized it becomes much more straightforward to modify the overall driver structure. This should help reduce the need for much of the copy/paste during new driver creation.

NOTE: This PR requires hardware validation. (The adis16448 driver is the first in this work because it is first in the imu directory.)

Describe problem solved by the proposed pull request
The IMU driver implementations all share a basic level of required functionality. Many implementations have been copy/pasted/modified but many use different file structures, use different names for methods that perform the same or similar operations, or have other small variations that can be standardized.

If the basic structure of all of the existing IMU drivers is standardized there should be opportunity to better architect driver inheritance architectures.

Describe your preferred solution
This PR breaks out accel/gyro/mag classes into their own files and establishes a basic file structure/class structure that can be replicated in each of the other IMU driver classes.

Describe possible alternatives
The driver functions as-is, so it is entirely acceptable to keep the status-quo. (Please let me know if that is preferred.)

Thanks for your review!

[dagar]

I can test this soon.

[mcsauder]

This PR, and #11629 are steps in the direction of #9279. I don't think that the drivers will all get cleaned up in one pass, so I think it's important to keep chipping away until they all have the same basic components, standardized naming, standardized method ordering, methods that do the same thing have the same lines of code, etc. Once the drivers are aligned, it will be very straightforward to implement inheritance structures and architectural modifications.

[mcsauder]

Closing in favor of #12066!