Usb serial (#1648)

* enabled usb clock
* added usb stack to application
* fixed pll0usb clock setup
* implemented serial usb handshake
* implemented serial communication
* integrated chibios shell
* implemented device reset
* implemented enter dfu mode
* implemented hackrf mode command
* implemented flash command
* implemented memory manipulation
* implemented button control
* fixed mode change
* improved reset behavior
* implemented directory commands
* implemented file commands
* improved data communication
* refactorings

firmware/application/event_m0.cpp

@@ -113,6 +113,7 @@ void EventDispatcher::run() {
     while (is_running) {
         const auto events = wait();
         dispatch(events);
+        portapack::usb_serial.dispatch();
     }
 }