MAINTAINERS: Saying goodbye to David Brownell

We had to say goodbye when David passed away recently.  David had a
huge impact on our community, both personally in the lives of the
people he worked with, and technically in the design and maintenance
of several subsystems.  He is greatly missed.

He also leaves behind a number of much loved subsystems now orphaned.
This patch updates the MAINTAINERS file for the areas that David was
responsible for and adds an entry for him to the CREDITS file.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Harry Wei <harryxiyou@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>