Add support to isohybrid-gpt for EFI boot

Tested and works fine under qemu using seabios and ovmf
$ qemu-system-x86_64 -enable-kvm -drive file=~/archlinux-2013.06.20-dual.iso
$ qemu-system-x86_64 -enable-kvm -drive file=~/archlinux-2013.06.20-dual.iso,media=cdrom
$ qemu-system-x86_64 -enable-kvm -bios ~/arch/OVMF/bios.bin -drive file=~/archlinux-2013.06.20-dual.iso
$ qemu-system-x86_64 -enable-kvm -bios ~/arch/OVMF/bios.bin -drive file=~/archlinux-2013.06.20-dual.iso,media=cdrom