dm: core: Add ofnode_get_chosen_prop()

Add a function to read a property from the chosen node, providing access
to its length. Update ofnode_get_chosen_string() to make use of it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/ofnode.c b/drivers/core/ofnode.c
index 4fc29a7..f55ef15 100644
--- a/drivers/core/ofnode.c
+++ b/drivers/core/ofnode.c
@@ -427,20 +427,25 @@
 		return offset_to_ofnode(fdt_path_offset(gd->fdt_blob, path));
 }
 
-const char *ofnode_read_chosen_string(const char *name)
+const void *ofnode_read_chosen_prop(const char *propname, int *sizep)
 {
 	ofnode chosen_node;
 
 	chosen_node = ofnode_path("/chosen");
 
-	return ofnode_read_string(chosen_node, name);
+	return ofnode_read_prop(chosen_node, propname, sizep);
 }
 
+const char *ofnode_read_chosen_string(const char *propname)
+{
+	return ofnode_read_chosen_prop(propname, NULL);
+}
+
 ofnode ofnode_get_chosen_node(const char *name)
 {
 	const char *prop;
 
-	prop = ofnode_read_chosen_string(name);
+	prop = ofnode_read_chosen_prop(name, NULL);
 	if (!prop)
 		return ofnode_null();