bhyve.8: Update and rearrange to improve readability

bhyve's man page is a very long block of text that has grown to
proportions that make it hard to read.  In particular, the level of
nesting of various content means man can no longer render the text in a
user-friendly way.

To remedy this:
- move the -s argument documentation into a separate section and
  reformat the various arguments so they are consistent
- add documentation on how to use the -o config.dump feature
- make the listing of various arguments more consistent
- consolidated duplicate listings of TPM backends
- add an example for the config.dump feature
- fix various formatting inconsistencies.

Reviewed by:	emaste, imp, jrm, Pau Amma <pauamma@gundo.com>, rgrimes
Differential Revision:	https://reviews.freebsd.org/D43940