Boeffla-Sound: Engine 1.4.9

- Completely neutralized mic_mode to avoid any interference to related registers
  when not used (fix for call issues with certain firmwares) by not doing any actions
  until mic_mode is enabled + using cached registers when restoring default mode back
- mic_mode is now exclusive and not "intelligent" anymore. If you want to make calls,
  switch mic_mode back to default first
- Safety-net introduced to avoid writing empty mic register cache values back to
  the registers in any case (thx to Yank555 for this idea)
- fix reported issue about boeffla sound starting up in enabled mode
  is causing a boot loop