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. 
This is only half of softreset detection: https://github.com/multiwii/baseflight/blob/5a87431bea51f2a2d922aa343c40407e3af2964c/src/drv_system.c#L200