libfdt: Add support for disabling ordering check/fixup

Add a way to remove this check and the reordering code, which is
unnecessary if the dtb is known to be correctly ordered.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200220214557.176528-8-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_rw.c

@@ -435,7 +435,8 @@ int fdt_open_into(const void *fdt, void *buf, int bufsize)
 			return struct_size;
 	}
 
-	if (!fdt_blocks_misordered_(fdt, mem_rsv_size, struct_size)) {
+	if (can_assume(LIBFDT_ORDER) |
+	    !fdt_blocks_misordered_(fdt, mem_rsv_size, struct_size)) {
 		/* no further work necessary */
 		err = fdt_move(fdt, buf, bufsize);
 		if (err)