ARM: dts: msm: disable secure cma on 8937

A big unused CMA region is not a good thing to have, eventhough
CMA pages can be used for movable allocations. It has a terrible
effect on page frame reclaim. So let us have secure CMA disabled,
and enable it when needed.

Change-Id: Id59402ab2d3f3dcca5f393c0d13237d3c196a61c
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>