libdmabufheap: Introduce AllocSystem() API am: f7b3d5df5d am: 5386f300c7 am: b7b662058c am: 86d06500c3

Original change: https://android-review.googlesource.com/c/platform/system/memory/libdmabufheap/+/1649887

Change-Id: Iac11641dc68664d83ae158e8fcf9010154deab7e
tree: ec0f0471d720e7d8a961cf4b4090c0ece8fdd84f
  1. include/
  2. tests/
  3. Android.bp
  4. BufferAllocator.cpp
  5. BufferAllocatorWrapper.cpp