[bug] Linux kernel menuconfig issue

symptom:
Makefile:434: *** mixed implicit and normal rules.  Stop.
Makefile:1551: *** mixed implicit and normal rules.  Stop.

root cause:
old Makefile format

solution:
(434) config %config: scripts_basic outputmakefile FORCE
(1551) / %/: prepare scripts FORCE

-->
(434) %config: scripts_basic outputmakefile FORCE
(1551) %/: prepare scripts FORCE

ref:
http://www.cnblogs.com/jevan/archive/2011/03/20/1989199.html