vmscan: prevent shrinking of active anon lru list in case of no swap space V3

shrink_zone() can deactivate active anon pages even if we don't have a
swap device.  Many embedded products don't have a swap device.  So the
deactivation of anon pages is unnecessary.

This patch prevents unnecessary deactivation of anon lru pages.  But, it
don't prevent aging of anon pages to swap out.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>