overlay: Allocate from MM heap as a fallback

 * Not all devices support IOMMU yet, so use the MM heap as a fallback.
 * Enabled when NO_IOMMU is set

Change-Id: I9d9f3dffb92f5b4bf45422df0f66a40611943202
Merge "overlay: Allocate from MM heap as a fallback" into qcom-4.4_2.7