mm: vmscan: support equal reclaim for anon and file pages

When performing memory reclaim support treating anonymous and
file backed pages equally.

Swapping anonymous pages out to memory can be efficient enough
to justify treating anonymous and file backed pages equally.

CRs-Fixed: 648984
Change-Id: I6315b8557020d1e27a34225bb9cefbef1fb43266
Signed-off-by: Liam Mark <lmark@codeaurora.org>