Edits to the driver-model documentation for grammar, clarity and content.

These docs haven't been updated in years, and some of the technical content
and discussion has become stale; this patch updates these.  In addition,
some of the language is awkward.  Fix this.

(I'm trying to cleanup the other files in this directory also,
patches for these will come a bit later).
Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Acked-by: Patrick Mochel <mochel@digitalimplant.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>