drm/msm/sde: enable ion for framebuffer object allocation

Enable internal framebuffer object allocation to use ion
allocator to support internal secure buffer allocation.

CRs-Fixed: 2009714
Change-Id: I3ea30ec6c495624d892c467b159a8584b0f0f82f
Signed-off-by: Alan Kwong <akwong@codeaurora.org>