[BSP] Update qemu nographic script

bsp/qemu-vexpress-a9/qemu-nographic.sh

@@ -1 +1,6 @@
-qemu-system-arm -M vexpress-a9 -kernel rtthread.elf -nographic
+if [ ! -f "sd.bin" ]; then
+dd if=/dev/zero of=sd.bin bs=64M count=1
+fi
+
+qemu-system-arm -M vexpress-a9 -kernel rtthread.elf -nographic -sd sd.bin
+