add qemu-nographic.sh

prebuilt/qemu-virt64-riscv/qemu-nographic.sh

+#!/bin/bash
+if [ ! -f "sd.bin" ]; then
+qemu-img create -f raw sd.bin 64M
+fi
+
+qemu-system-riscv64 -nographic -machine virt -m 256M -kernel rtthread.bin \
+-drive if=none,file=sd.bin,format=raw,id=blk0 -device virtio-blk-device,drive=blk0,bus=virtio-mmio-bus.0 \
+-netdev user,id=tap0 -device virtio-net-device,netdev=tap0,bus=virtio-mmio-bus.1 \
+-device virtio-serial-device -chardev socket,host=127.0.0.1,port=4321,server=on,wait=off,telnet=on,id=console0 -device virtserialport,chardev=console0