image: Add fallback for fit_config_verify

Add a fallback for this function so it can be used without regard to
whether FIT_SIGNATURE is enabled or not.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/image.h b/include/image.h
index b6a8098..6f9c5a4 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1259,7 +1259,14 @@
 			       size_t size);
 
 int fit_image_verify(const void *fit, int noffset);
+#if CONFIG_IS_ENABLED(FIT_SIGNATURE)
 int fit_config_verify(const void *fit, int conf_noffset);
+#else
+static inline int fit_config_verify(const void *fit, int conf_noffset)
+{
+	return 0;
+}
+#endif
 int fit_all_image_verify(const void *fit);
 int fit_config_decrypt(const void *fit, int conf_noffset);
 int fit_image_check_os(const void *fit, int noffset, uint8_t os);