build: Remove "fwdebug" and "common" feature flags

This simplifes the buld and checks with very little overhead and the
fwdebug device is I/O port device on 0x402 that can be used by edk2 as a
very simple character device.

See: #4679

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

vmm/src/device_manager.rs

@@ -1560,9 +1560,7 @@ impl DeviceManager {
                 .io_bus
                 .insert(cmos, 0x70, 0x2)
                 .map_err(DeviceManagerError::BusError)?;
-        }
-        #[cfg(feature = "fwdebug")]
-        {
+
             let fwdebug = Arc::new(Mutex::new(devices::legacy::FwDebugDevice::new()));
 
             self.bus_devices