MFC r303113: Cross-link some SMBus controller drivers man pages.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

mdoc: terminate quoted strings.

Reviewed by: brueffer

Revise markup.

I'm about to merge these only now, so correct the first release
of their appearence to be 6.2.

Add basic manpages for amdsmb(4) and nfsmb(4).