x86: Panic when SPL or TPL fail

At present when these fail to boot there is no message, just a hang. Add a
panic so it is obvious that something when wrong.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/lib/tpl.c b/arch/x86/lib/tpl.c
index cfefa78..d70f590 100644
--- a/arch/x86/lib/tpl.c
+++ b/arch/x86/lib/tpl.c
@@ -55,7 +55,7 @@
 	ret = x86_tpl_init();
 	if (ret) {
 		debug("Error %d\n", ret);
-		hang();
+		panic("x86_tpl_init fail");
 	}
 
 	/* Uninit CAR and jump to board_init_f_r() */