Support option to add defmt to print signal enums for debugging on target

[wallem89]

I would like to see a feature which gives the ability to print signals with an enum with no_std right away.

This can be done with defmt to format the enum values so they can be printed for debugging.

This is option can be always on but for flexibility one could consider place this behind an optional flag to enable this feature when necessary.

See PR #87 for my proposal.