[BSP][QEMU]fix run error on mac add dbg.sh on linux

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

+if [ ! -f "sd.bin" ]; then
+dd if=/dev/zero of=sd.bin bs=1024 count=65536
+fi
+
+
+qemu-system-arm -M vexpress-a9 -kernel rtthread.elf -serial vc -serial vc -sd sd.bin -S -s
\ No newline at end of file

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

 if [ ! -f "sd.bin" ]; then
-dd if=/dev/zero of=sd.bin bs=64M count=1
+dd if=/dev/zero of=sd.bin bs=1024 count=65536
 fi
 
 qemu-system-arm -M vexpress-a9 -kernel rtthread.elf -nographic -sd sd.bin -net nic -net tap

bsp/qemu-vexpress-a9/qemu.sh

 if [ ! -f "sd.bin" ]; then
-dd if=/dev/zero of=sd.bin bs=64M count=1
+dd if=/dev/zero of=sd.bin bs=1024 count=65536
 fi
 
 qemu-system-arm -M vexpress-a9 -kernel rtthread.elf -serial stdio -sd sd.bin