clean kernel

kernel clean 分为三个lever的clean，即make clean -> make mrproper -> make distclean
clean的东西逐步增多，详细描述如下：
make clean     Delete most generated files
               Leave enough to build external modules
make mrproper  Delete the current configuration, and all generated files
make distclean Remove editor backup files, patch leftover files and the like
从源码也可以看出make clean -> make mrproper -> make distclean
clean: archclean vmlinuxclean
mrproper: clean archmrproper $(mrproper-dirs)
    $(call cmd,rmdirs)
    $(call cmd,rmfiles)

distclean: mrproper

    @find $(srctree) $(RCS_FIND_IGNORE) \
        \( -name '*.orig' -o -name '*.rej' -o -name '*~' \
        -o -name '*.bak' -o -name '#*#' -o -name '.*.orig' \
        -o -name '.*.rej' -o -name '*%'  -o -name 'core' \) \
        -type f -print | xargs rm -f