Add VA_STATUS_ERROR_UNIMPLEMENTATION string representation.

src/va.c

@@ -311,6 +311,8 @@ const char *vaErrorStr(VAStatus error_status)
             return "invalid parameter";
         case VA_STATUS_ERROR_RESOLUTION_NOT_SUPPORTED:
             return "resolution not supported";
+        case VA_STATUS_ERROR_UNIMPLEMENTED:
+            return "the requested function is not implemented";
         case VA_STATUS_ERROR_UNKNOWN:
             return "unknown libva error";
     }