target: init: Correct few macros w.r.t AVB v2.0

Correct few macros in AVB v2.0 code path and also adds
function declarations which is used across multiple files.

Change-Id: Icca7fe5cca50f4f4ba530327d0cc41f1050ee2fb
diff --git a/include/target.h b/include/target.h
index 7b92dfb..2151f05 100644
--- a/include/target.h
+++ b/include/target.h
@@ -33,6 +33,7 @@
 {
 	VB_L = 1,
 	VB_M = 2,
+	VB_AVB2 = 4,
 };
 
 /* Target helper functions exposed to USB driver */