common: add some l0/l1 support in helpers
common: add some l0/l1 support in helpers

give l0/l1 some love - l0/l1 are a bit specific regarding keys,
bits, and lock registers.

Also make handling of f0/f1 explicit: ultimate goal is to have some
sanity check and clear codepath in that code in case some new target
is added - and that the whole code uses these helpers.

some work should be done to refactor a bit the flash register mapping
based on family, but not yet.

lo lock

simonjwright/stlink,simonjwright/stlink