It's time to abandon MBR installations on
ARM64 platforms.

Obtained from:         Semihalf
Submitted by:          Dominik Ermel <der@semihalf.com>
Sponsored by:          Cavium
Reviewed by:           gjb, emaste, marcel
Approved by:           re (gjb)
Differential Revision: https://reviews.freebsd.org/D6798