MFC r271563:
Make the root-on-zfs part of the installer warn a user who booted the
installer via UEFI that we do not support booting ZFS via UEFI yet

PR:		193595
Approved by:	re (gjb), nwhitehorn
Sponsored by:	ScaleEngine Inc.
MFC r271676, r271677, r271678:

r271676:
  Catch up with Crochet changes to fix the BEAGLEBONE
  build.

r271677:
  Catch up with Crochet changes to fix the WANDBOARD-QUAD
  build.

r271678:
  Set a static revision of the Crochet checkout to avoid
  surprise build failures.

Approved by:	re (marius)
Sponsored by:	The FreeBSD Foundation