This puts genksyms into scripts/genksyms/.

genksyms used to be maintained externally, though the only possible user
was the kernel build. Moving it into the kernel sources makes it easier to
keep it uptodate, like for example updating it to generate linker scripts
directly instead of postprocessing the generated header file fragments 
with sed, as we do currently.

Also, genksyms does not handle __typeof__, which needs to be fixed since
some of the exported symbol in the kernel are defined using __typeof__. 

(Rusty Russell/me)