o Add BERI Virtio Networking Frontend (if_vtbe)
o Move similar block/networking methods to common file
o Follow r275640 and correct MMIO registers width
o Pass value to MMIO platform_note method.

Sponsored by:	DARPA, AFRL


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275647 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f