build - Add the 'efisetup' script

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.