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: I1382381134db21435ca725d0e2c2b3194da16f38
gralloc: our prebuilt camera lib needs the ADSP/CAMERA heap to be first

Change-Id: I51760c306a1f96ba170cb052589199c246e296a2