x86: coreboot: Add timestamps from coreboot to bootstage

Receiving timestamps from coreboot was unceremoniously dropped some time
ago. Add it back.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 8ad01ce36f7 ("x86: Remove x86 specific GD flags as they are...")

arch/x86/cpu/coreboot/coreboot.c

@@ -77,6 +77,8 @@ static void board_final_init(void)
 
 static int last_stage_init(void)
 {
+	timestamp_add_to_bootstage();
+
 	if (IS_ENABLED(CONFIG_XPL_BUILD))
 		return 0;