data tree REFCTOR move prefix callbacks to plugins types

Meaning they are still public but needed only when
implementing plugins. Common API functions do not
require these callbacks.
diff --git a/src/parser_xml.c b/src/parser_xml.c
index cb1955d..0254a81 100644
--- a/src/parser_xml.c
+++ b/src/parser_xml.c
@@ -246,7 +246,7 @@
         assert(xmlctx->status == LYXML_ELEM_CONTENT);
         if (i < key_set.count) {
             /* validate the value */
-            r = lys_value_validate(NULL, snode, xmlctx->value, xmlctx->value_len, lydxml_resolve_prefix, xmlctx, LYD_XML);
+            r = _lys_value_validate(NULL, snode, xmlctx->value, xmlctx->value_len, lydxml_resolve_prefix, xmlctx, LYD_XML);
             if (!r) {
                 /* key with a valid value, remove from the set */
                 ly_set_rm_index(&key_set, i, NULL);
@@ -369,7 +369,7 @@
 
         if ((*snode)->nodetype & LYD_NODE_TERM) {
             /* value may not be valid in which case we parse it as an opaque node */
-            if (lys_value_validate(NULL, *snode, xmlctx->value, xmlctx->value_len, lydxml_resolve_prefix, xmlctx, LYD_XML)) {
+            if (_lys_value_validate(NULL, *snode, xmlctx->value, xmlctx->value_len, lydxml_resolve_prefix, xmlctx, LYD_XML)) {
                 *snode = NULL;
             }
         } else {