brightness, wired LAN power and bass gain), and update the description of
one previously unknown feature (display contrast). While here, expand on
a comment and remove two defines left over from an old version of the code.
Also update man page to document the above changes, and correct grammar.
PR: kern/127581
too, so, instead of descending to the i386 directory, we add some magic to
the parent Makefile.
These man pages refer to drivers that I'm aware that work on amd64. Most
likely there are more, but I'll deal with them later.
Approved by: brueffer, philip, takawata
