gralloc: Allow legacy devices to use PMEM for ADSP (camera).

Partially bring back PMEM support for legacy devices having proprietary
camera
libraries stuck in PMEM. This change allows these devices to continue
using
PMEM for the camera, and ION for everything else.

Change-Id: I1afbc7d137b3d49b2ab3e53917b16fd920ea140b

Blefish/android_hardware_qcom_display-caf@41c5131