dtc: introduce label relative path references

Since introduction of OF_UPSTREAM flag, U-Boot's dtc must be able
to compile Kernel's device tree.

Since kernel commit 7de129f5389b ("ARM: dts: stm32: stm32mp151a-prtt1l:
Fix QSPI configuration"), label relative path references has been
introduced. These label relative path references is not supported
by current U-Boot dtc version 1.5.0: (see mailing list discussion [1]).

In order to support such label relative patch references
adds following commit from upstream DTC tree:

commit 651410e54cb9 ("util: introduce xstrndup helper")
commit ec7986e682cf ("dtc: introduce label relative path references")

[1] https://lore.kernel.org/all/20250115144428.GZ3476@bill-the-cat/T/

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/dtc/dtc-parser.y b/scripts/dtc/dtc-parser.y
index 011a5b2..b3b9c83 100644
--- a/scripts/dtc/dtc-parser.y
+++ b/scripts/dtc/dtc-parser.y
@@ -34,6 +34,12 @@
 
 extern struct dt_info *parser_output;
 extern bool treesource_error;
+
+static bool is_ref_relative(const char *ref)
+{
+	return ref[0] != '/' && strchr(&ref[1], '/');
+}
+
 %}
 
 %union {
@@ -176,12 +182,17 @@
 			 */
 			if (!($<flags>-1 & DTSF_PLUGIN))
 				ERROR(&@2, "Label or path %s not found", $1);
+			else if (is_ref_relative($1))
+				ERROR(&@2, "Label-relative reference %s not supported in plugin", $1);
 			$$ = add_orphan_node(name_node(build_node(NULL, NULL), ""), $2, $1);
 		}
 	| devicetree DT_LABEL DT_REF nodedef
 		{
 			struct node *target = get_node_by_ref($1, $3);
 
+			if (($<flags>-1 & DTSF_PLUGIN) && is_ref_relative($3))
+				ERROR(&@2, "Label-relative reference %s not supported in plugin", $3);
+
 			if (target) {
 				add_label(&target->labels, $2);
 				merge_nodes(target, $4);
@@ -197,6 +208,8 @@
 			 * so $-1 is what we want (plugindecl)
 			 */
 			if ($<flags>-1 & DTSF_PLUGIN) {
+				if (is_ref_relative($2))
+					ERROR(&@2, "Label-relative reference %s not supported in plugin", $2);
 				add_orphan_node($1, $3, $2);
 			} else {
 				struct node *target = get_node_by_ref($1, $2);