bhyve: use physical lobits for BARs of passthru devices

Tell the guest whether a BAR uses prefetched memory or not for
passthru devices by using the same lobits as the physical device.

Reviewed by: grehan
Sponsored by: Beckhoff Autmation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D32685

(cherry picked from commit e87a6f3ef284593c01e0fd3f8b5bfc1f645e5b18)