vmm: Support both reset and shutdown

Add a 2nd EventFd to the VM to control resetting (rebooting) the VM this
supplements the EventFd used for managing shutdown of the VM.

The default behaviour on i8042 or triple-fault based reset is currently
unchanged i.e. it will trigger a shutdown.

In order to support restarting the VM it was necessary to make start()
function take a reference to the config.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

devices/src/legacy/i8042.rs

@@ -34,6 +34,7 @@ impl BusDevice for I8042Device {
 
     fn write(&mut self, _base: u64, offset: u64, data: &[u8]) {
         if data.len() == 1 && data[0] == 0xfe && offset == 3 {
+            debug!("i8042 reset signalled");
             if let Err(e) = self.reset_evt.write(1) {
                 error!("Error triggering i8042 reset event: {}", e);
             }