bsp-guide: Removed deprecated tool sections

bsp-guide: Removed deprecated tool sections

I took out the sections at the end of the manual that talked
about the yocto-kernel tool.  This tool is no longer maintained
and there is no equivalent tool.  I also fixed the yocto-bsp
tool to be the bitbake-layers tool.  This involved some
consolidation of sections.

I fixed some links in the kernel-dev and toaster-manual.

(From yocto-docs rev: 20cda99b301b6327d816c4a4cfb3511ad25c987c)

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