sfxge(4): prepare for moving EF10 definitions to ef10_impl.h

Move legacy privilege masks near to their only user.
Move Huntington definitions to the top of hunt_impl.h to prepare
for moving the remaining EF10 definitions to ef10_impl.h.

Submitted by: Andy Moreton <amoreton at solarflare.com>
Sponsored by: Solarflare Communications, Inc.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D6343