Makefile: revert "Makefile: Document ability to make file.lst and file.S" partially

Commit 62718979 ("Makefile: Document ability to make file.lst
and file.S") document ability to make file.S, but there isn't such
ability in kbuild, so revert it.

Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>