use the multiboot info passed from the bootloader to the kernel.

If the magic number 0x2BADB002h doesn't match, we can't trust the bootinfo struct either. The next step is to get rootdevice from the bootloader command line (kernel LetkuOS.krn rootdevice=hda2) so we know which drive and partition to mount as C:\ (this is the way LetkuOS will do it at start)