- Add missing semaphore take on bus
- Initialize device on init function rather than constructor: the
constructor may run before I2CDeviceManager is initialized since our
AP_Notify objects are static so it can't be used.
Due to the way the headers are organized changing a single change in
an AP_Notify driver would trigger a rebuild for most of the files in
the project. Time could be saved by using ccache (since most of the
things didn't change) but we can do better, i.e. re-organize the headers
so we don't have to re-build everything.