PR#141 from David Leonard <d@occult.fnarg.net.au> with some small mods by

PR#141 from David Leonard <d@occult.fnarg.net.au> with some small mods by
me.
- Provide option (enabled in GENERIC and GENERICSBC) to disable ADB
  configuration when serial console is enabled.  Old behavior allows
  booting even if ADB probe hangs (Apple had several ways to access
  ADB).
- Configure ite0 differently--don't assume that it's only extant if it
  is the console.