Replace MemoryDealer in AudioFlinger

MemoryDealer can cause internal fragmentation and provides
somewhat arbitrary memory limitations for clients of AudioFlinger.

Replace with composable allocator allowing for flexible allocation
policies. Return deallocated pages to kernel.

Test: atest shared_memory_allocator_tests, atest AudioTrackTest, atest
AudioRecordTest

Bug: 139061005
Change-Id: Ifde23c6024b2ad11ddf1960b572a91e8eedfdb79