mcu: Support reset command

Extend the FIRMWARE_RESTART command so that it can use the firmware
"reset" command instead of the "arduino" mechanism.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/msgproto.py

@@ -184,6 +184,7 @@ class UnknownFormat:
         return {'#msgid': msgid, '#msg': msg}, len(s)-MESSAGE_TRAILER_SIZE
 
 class MessageParser:
+    error = error
     def __init__(self):
         self.unknown = UnknownFormat()
         self.messages_by_id = {}