[gps] refactor sending of SVINFO

- when using only GPS or GPS_INT messages:
  send SVINFO for all satellites while no GPS fix,
  after 3D fix, send avialable sats only when there is new information
- possibility to add SVINFO to periodic telemetry, sends it for all sats
[rotorcraft] fix USE_KILL_SWITCH_FOR_MOTOR_ARMING
[conf] asctec_cdw bugfix
Merge pull request #1038 from paparazzi/fix_kill_switch_arming

[rotorcraft] fix USE_KILL_SWITCH_FOR_MOTOR_ARMING
second release candidate for next stable release v5.4
[rotorcraft] switching to MODE_MANUAL allowed even during HOME_MODE