fix: Various mostly X10E soft serial issues (#3382)

* fix: pulse driver with 32bit timers

* fix(mpm): clear RX buffer before signature

* fix: add some debouncing on soft-serial start bit detection

This helps coping with spurious impulses on S.PORT created by payload sent over PPM pin (X10E).

* fix: whenever the RXNE bit is set, read the register

... regardless of errors. That allows for reducing the effect of detected errors.

radio/src/io/multi_firmware_update.cpp

@@ -233,6 +233,8 @@ const char * MultiFirmwareUpdateDriver::waitForInitialSync()
 
 const char * MultiFirmwareUpdateDriver::getDeviceSignature(uint8_t * signature) const
 {
+  clear();
+
   // Read signature
   sendByte(STK_READ_SIGN);
   sendByte(CRC_EOP);