Add framework for Spark Core board support.  The initial commit is a clone of the Maple Mini and still needs Spark customizations

Add a new method to the USB host driver interface:  getdevinfo.  This method will return information about the currently connected device.  At present, it only returns the device speed.  The speed is needed by the enumeration logic in order to set a credible initial EP0 max packet size

Separate wait() and enumerate() methods from struct usbhost_driver_s and move to new interface, struct usbhost_connection_s.  This is part of the necessary restructuring of the USB host interface to support multiple root hub ports.

Add an NSH configuration for the Arduino Due; Pluse several fixes related to the Due and to the SAM3X in general