mm: memcontrol: allow swappiness above 100

Allow swappiness > 100, to prefer swapping over file reclaim.
This is beneficial for use cases with fast swap devices like zram.
Limit the swappiness to <= 200 to avoid an unsigned underflow in
shrink_lruvec, and restrict to non-root cgroups.

CRs-Fixed: 988758
Change-Id: I4212590a6fad6fdbeb6664e42aa10f7ec1ce961d
Signed-off-by: Kishore Srivenkata Ganesh Bolisetty <bsrivenk@codeaurora.org>
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>