MAINTAINERS: Add some missing directories or files

In a few cases we have MAINTAINERS entries that are missing obvious
paths or files. Typically this means a board directory that did not list
itself, but in a few cases we have a Kconfig file or similar.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>