调整脚本,使得能够创建riscv的磁盘镜像,并引导进入riscv下的grub (#450)

* 安装musl toolchain以及riscv相关的工具链

* 调整脚本,使得能够创建riscv的磁盘镜像,并引导进入riscv下的grub

```shell
export ARCH=riscv64
make write_diskimage
make qemu
```

即可在serial_opt.txt看到进入grub的提示信息

tools/mount_virt_disk.sh

@@ -5,7 +5,19 @@ if [ ! $uid == "0" ];then
  exit
 fi
 
-LOOP_DEVICE=$(losetup -f --show -P ../bin/disk.img) \
+# 检查是否设置ARCH环境变量
+
+if [ ! ${ARCH} ];then
+ echo "请设置ARCH环境变量"
+ exit
+fi
+
+
+DISK_NAME=disk-${ARCH}.img
+
+echo "Mounting virtual disk image '${DISK_NAME}'..."
+
+LOOP_DEVICE=$(losetup -f --show -P ../bin/${DISK_NAME}) \
     || exit 1
 
 echo ${LOOP_DEVICE}p1