and call it at the end of mcu_init
This should be used to init board functions like killing other processes on the Parrot drones
or initializing other onboard peripherals like the cmos cam chips.
So we use this instead of killing progs in electrical_init.
Replaces #1251 and is related to #1252
This is a kludge until we can better leverage threads and have real events.
Without this limit the event flags will constantly polled as fast as possible,
resulting on 100% cpu load on boards with an (RT)OS.
On bare metal boards this is not an issue, as you have nothing else running anyway.
Enable this for the bebop and ardrone2 by default.
Alternative to #1239 and should fix#1233
