Spektrum Satelitte bind code ported from Baseflight

includes support for a hardware bind plug (PB5 pin 41)
Activate via OPTIONS="HARDWARE_BIND_PLUG" during make
The bind code will only work for the default serial RX (USART2) port. 
I have take some deeper look into this. I have changed the code for the STM32F1 based targets. can not find anything how to detect a soft reset for the STM32F3xx. For now I created a dummy function which always returns false. Normally this should all work for now but I would prefer to test this with an receiver by my self in all variations. It think the save way for now would be to go forward an remove the automatic disabling of the bind function. The bind part itself is well tested and is working. I can go ahead in a second phase if my receiver arrives to test the more advanced features like automatic disable if the RX has properly bond. Your feedback is appreciated. If someone else can do this testing I can update the pull request and publish the new code.