patches/RELENG_8_3: Update virtio with from 8-STABLE

This brings the virtio drivers to the identical level of FreeBSD 8.4
plus an additional patch obtained from master which fixes issues seen
with QEMU 1.4 onwards.

This also switches the virtio patchset into one large patch similar
to what was done with mfi.
Merge pull request #124 from matsimon/virtio-sync

patches/RELENG_8_3: Update virtio with from 8-STABLE