When a gyro driver is stopped, the topic is unadvertised and
orb_group_count() returns a smaller count. This can have the effect, that
we poll on a certain gyro fd, but since _gyro.subscription_count is reduced
we never do the orb_copy for that fd.

This cannot happen when armed. And only someone playing with the shell
can trigger it (sensor failures do not have that effect).

This makes sure that poll() never returns immediately.
accel & mag are only updated to keep the code in sync.

Should some of these be of interest to someone, we should create a profile.

Copy/paste logic in rc.interface to group MIXER and MIXER_AUX logic, alphabetize hardware list in rc.interface, alphabetize set/unset lists in rcS, and add -p argument to pwm failsafe calls per issue #9775.

Group instances of UAVCAN logic into a single block and copy/paste/regroup OUTPUT_MODE logic to form on block of code handling OUTPUT_MODE.

   FMUv5 has singlewire support

   This is a stubbed out version that will rely on the hardware
   manifest moving forward.

    - sitl_gazebo in PX4/Firmware (a08fc0c3ff3cfb4bba57035c98b0a7398b0c2a19): https://github.com/PX4/sitl_gazebo/commit/ac54b8fdddd9b21dbe6d59deaf46494864858bc9
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/c1ca87e37b831cd4b64ac642957e701875738909
    - Changes: https://github.com/PX4/sitl_gazebo/compare/ac54b8fdddd9b21dbe6d59deaf46494864858bc9...c1ca87e37b831cd4b64ac642957e701875738909

    c1ca87e 2018-07-16 Elia Tarasov - add support for gazebo version greater or equal 9
eb4494d 2018-07-16 Elia Tarasov - load rotation signs from sdf model file
c00b9ee 2018-07-16 Elia Tarasov - add default constants for rotation signs
36360c5 2018-07-16 Elia Tarasov - add rotation signs to class variables