MFC r307517, r314342, r316357, r317545, r317777:

r307517:
Typo fixed: arbitraty -> arbitrary.
PR: 213559

r314342:
bhyve: document virtio-console in the manpage

r316357:
Minor style improvements in bhyve.8
Replace "as of now" with "at present". As the change is a really minor one,
don't bump .Dd.

r317545:
Document raw framebuffer device and XHCI device configurations.

r317777:
Improve documentation of fbuf device.

Approved by: grehan (mentor)
Approved by: re (gjb)