defconfig: msm: sdm660: disable memory cgroups

Memory cgroups is an unused feature on sdm660. But
enabling it in kernel means that user space can
configure it. Avoid such user configurations until
the feature is decided to be deployed.

Change-Id: Ie77a4de51a59179ff3cb543e3cc955ce48412a59
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>