dtc: Mark various internal functions static

Signed-off-by: Josh Triplett <josh@joshtriplett.org>

scripts/dtc/libfdt/fdt_ro.c

@@ -411,7 +411,7 @@ int fdt_node_offset_by_phandle(const void *fdt, uint32_t phandle)
 					     &phandle, sizeof(phandle));
 }
 
-int _stringlist_contains(const char *strlist, int listlen, const char *str)
+static int _stringlist_contains(const char *strlist, int listlen, const char *str)
 {
 	int len = strlen(str);
 	const char *p;