mmaps: fields coverage

[burrbull]

cc @adamgreig
What do you think about this?

[adamgreig]

It would be useful in reviewing PRs to see changes in field coverage, but I don't know if it should put another line of output on the mmap command. Maybe it could be its own coverage command, or maybe it could output field coverage per-register and per-peripheral at the end of their existing lines?

0x10000000 A PERIPHERAL PeriphA (2/3 fields covered)
0x10000010 B  REGISTER REG1: Register A1 (2/2 fields covered)

[burrbull]

Maybe it could be its own coverage command

This was my initial idea but then I understood there is not real advantage.

maybe it could output field coverage per-register and per-peripheral at the end of their existing lines

per-peripheral should be enough for me.
Per-register entries cause ultra big diffs as for me and hide more valuable changes and fixes.
Also it makes sense to have shorthand for full or zero coverage (or both) to make mmaps cleaner.