dev-manual, mega-manual: Updated kernel overview tree structure figure

This figure was a bit out of date.  I updated a few of the file
names.  Figure needs to reside in the Figures folder of both the
dev-manual and the mega-manual.

(From yocto-docs rev: 1e76477810b6be095f9ca190c9a8f0276ee4b8f9)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>