cas-vts: use MemoryDealer to allocate shared memory

cas hal can't (and doesn't need to) use hidl_memory allocated by
hidl allocator. All real clients (MediaDescrambler jni, ACodec)
are using MemoryDealer-allocated ashmem only. Modify the test
to cover these cases.

bug: 67603039
test:
> make vts -j64
> vts-tradefed run vts -m VtsHalCasV1_0Target

Change-Id: Ib9563abc1a14c34781a28d15c7766c6c160d288a