change(boot.img): use 512MiB as the disk image size

CMakeLists.txt

@@ -132,7 +132,7 @@ add_custom_target(boot.img
     DEPENDS mbr_hole.bin
     COMMAND dd if=mbr.bin of=boot.img
     COMMAND cat mbr_hole.bin >> boot.img
-    COMMAND dd if=/dev/zero of=boot.img bs=`expr 32 \\* 1024 \\* 1024` count=0 seek=1
+    COMMAND dd if=/dev/zero of=boot.img bs=`expr 512 \\* 1024 \\* 1024` count=0 seek=1
     COMMAND echo -n 'n\\n\\n\\n\\n\\na\\nw\\n' | fdisk boot.img
     COMMAND mkfs.fat --offset=2048 -v -n SYSTEM boot.img
 )