Aligns *.h and *.c to underscore naming convention.
These were kept (with warnings) for backwards compatibility with external boards/shields:
- kscan-mock.h
- matrix-transform.h
They should be removed in the future.
PR: #523
The Quefrency board has two options for each left and right half,
resulting in 4 unique combinations. This has been noted in the
overlay and dtsi files.
