adf435x: rephrase table lookups for display texts

adf435x: rephrase table lookups for display texts

Try a different presentation of exising information in the register
fields' display text construction (extra parsers for known fields).
Attempt a source code format which hopefully better lends itself to
index range verification during review.

Make the number of available expansion texts stand out more visually,
so that readers can compare their count to the register field's width.
Address those register fields with four or more expansion values, keep
the simple single bit cases as they are. Add a comment for awareness.