Documentation: update kbuild make examples#2 to reflect changes

Update section 3.2 and 3.5 example, along with text in section 3.5
to reflect change.

Signed-off-by: matt mooney <mfm@muteddisk.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>