Split volume key verification and device activation.

It makes key verification easier and also allows digest
verification for keys not assigned to device segment
(unbound keys) for more keyslot context types (tokens).

lib/internal.h

@@ -263,4 +263,8 @@ static inline bool uint64_mult_overflow(uint64_t *u, uint64_t b, size_t size)
 	return false;
 }
 
+#define KEY_NOT_VERIFIED -2
+#define KEY_EXTERNAL_VERIFICATION -1
+#define KEY_VERIFIED 0
+
 #endif /* INTERNAL_H */