build - Add the 'efisetup' script
* Add the 'efisetup' script to /usr/sbin. This script is capable of
creating a pristine UEFI bootable DragonFlyBSD installation on the
target drive. The target drive will be wiped.
Note that this script does only a basic installation... literally once
it sets up the partitions it just does an installworld, make distribution,
and installkernel, and then some minor adjustments to create the initial
/etc/rc.conf, /etc/fstab, and /boot/loader.conf.
* Requires that you previously did a buildworld and buildkernel
before running the script.