Provide an interface to query dmabuf GPU allocations

The DMA buffers mapped by GPU device(s) are already accounted for
in the total exported dmabuf size (ionHeap) size.

To remove GPU memory from lost RAM, provide an API to get only the
DMA buf memory mapped by the GPU device(s).

Bug: 176477627
Test: adb shell dumpsys meminfo
Change-Id: Ie72f46c8de026b143629406714f413677ce6693b
Merged-In: Ie72f46c8de026b143629406714f413677ce6693b