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
gralloc: our prebuilt camera lib needs the ADSP heap to be first
gralloc: Fix PMEM heap allocation for 3.0 kernels

This is needed for PMEM camera libraries.

Symptoms: gralloc gives an error saying invalid argument to map /dev/pmem_adsp, and dmesg says that ION is trying to mmap it. This issue is likely being caused by the ION drivers in the 3.0 kernel as this issue does not exist with 3.4 kernels.

Signed-off-by: Sultanxda <sultanxda@gmail.com>