Add standard SYNOPSIS wording, fix typos, contractions and new sentence -> new line.
After r264897 restore the ability to add bootoptions from FDT for
platforms which do not use loaders or kernels that want to hardcode
options or for FDT passed in by loader.

Also fix a build issue by putting the kmdp variable accessed back under
the #ifdef FDT;  we may wish to revisit decision in which case more
code needs changing.

Submitted by:	brooks