kernel makefile:
 * eliminate code clones
 * while compiling kernel do not set KERNEL_LAYOUT at all instead of setting it to a dummy value (refs r9981)
 * document the reason for doing so


git-svn-id: file:///var/svn/freetz/trunk@9982 149334a1-2f27-0410-a3b9-fc62619ac1e6