[rotorcraft] auto-enable UNLOCKED_HOME_MODE if HOME mode is used on RC

If you set MODE_AUTO1 or MODE_AUTO2 of the RC mode switch to AP_MODE_HOME
you can't get out of HOME mode again via RC by default, only via GCS.
So if you really want to be able to switch to HOME mode via RC,
enable UNLOCKED_HOME_MODE by default.

See also #823