[configs/releng] Add SecureBoot support via prebootloader

Tested only under QEMU using OVMF SecureBoot enabled firmware plus lockdown-ms.

Both loader.efi (gummiboot) and vmlinuz.efi should be hashed before boot in secure mode.

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>
[archiso] 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

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>