Add macros for unchunked ext.msg. supported

lib/include/pd.h

 #define PD_RDO_USB_COMMS (1 << PD_RDO_USB_COMMS_SHIFT)
 #define PD_RDO_NO_USB_SUSPEND_SHIFT 24
 #define PD_RDO_NO_USB_SUSPEND (1 << PD_RDO_NO_USB_SUSPEND_SHIFT)
+#define PD_RDO_UNCHUNKED_EXT_MSG_SHIFT 23
+#define PD_RDO_UNCHUNKED_EXT_MSG (1 << PD_RDO_UNCHUNKED_EXT_MSG_SHIFT)
 
 #define PD_RDO_OBJPOS_SET(i) (((i) << PD_RDO_OBJPOS_SHIFT) & PD_RDO_OBJPOS)