创建，添加sdram

rt-thread/libcpu/xilinx/microblaze/cpu.c

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2006-2022, RT-Thread Development Team
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ * 2006-08-23     Bernard      first version
+ */
+
+#include <rtthread.h>
+