[PATCH] kbuild: fix split-include dependency

Splitting of autoconf.h requires that split-include was built before,
and
needs to be-re-done when split-include changes. This dependency was
previously missing. Additionally, since autoconf.h is (suppoosed to
be)
generated as a side effect of executing config targets, include/linux
should be created prior to running the respective sub-make.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>