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
2 files changed