update host example, add pio-pico-usb for rp2040

src/common/tusb_common.h

@@ -75,6 +75,12 @@
 
 #include "tusb_timeout.h" // TODO remove
 
+enum
+{
+  TU_INDEX_INVALID_8 = 0xFFu
+};
+
+
 //--------------------------------------------------------------------+
 // Optional API implemented by application if needed
 // TODO move to a more ovious place/file