C2Allocator: protetct memory mappings from race condition Protect memory mappings of C2DmaBufAllocator from race condition. Clean up C2AllocatorIon also. Bug: 213850092 Merged-In: Icf6d00491438176e9092b67974a9388e803ac130 Change-Id: Icf6d00491438176e9092b67974a9388e803ac130 (cherry picked from commit 530a22aaa005efbc51b5a283601c9c7872f2d757) (cherry picked from commit 5cbca291a6d288fa6d471c0dc223537ca12700d3) Merged-In: Icf6d00491438176e9092b67974a9388e803ac130