ANDROID: GKI: mm: vmstat: add pageoutclean

vmstat events currently count pgpgout, but that includes
only the writebacks, and not the reclaim of clean
pages. Add an event to count clean page evictions. This is
helpful to evaluate page thrashing cases.

Bug: 151963988
Test: build
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
(cherry picked from commit f15713432cbe85742b1ffc9db00ace1b2d6acd80)
[surenb: cherry-picked to resolve ABI diffs caused by vm_event_item enum]
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I113cfce495b5b70f0cef88c8425c7252e01291fe