bhyve: import OpRegion definitions

Those definitions are required for the GVT-d emulation to parse the
OpRegion.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D40037

(cherry picked from commit b67f0d360b87d6e8a71ab5118a8acb350505c20a)