audio: Add stub default MMAP implementation

Add support for MMAP simulation to the default
implementation. Since there is no support for MMAP audio I/O on
CVD, the implementation is a stub.

The implementation supports 'createMmapBuffer' operation via
vendor property 'aosp.createMmapBuffer'. VTS tests for MMAP
streams are enabled back for this case (and for upcoming API
V4). VTS calls 'createMmapBuffer' after the stream has
transitioned out from the 'STANDBY' state.

Also, VTS for MMAP updated to wait for the burst size duration
after each 'burst' command in order to simulate audio I/O flow
and ensure that the stream positions get eventually updated.

Note that even with 'createMmapBuffer', the HAL implementation
must still provide some valid shared memory FD when opening an MMAP
stream. This is a limitation due to the requirement of the HAL
API on the descriptor being "non-null". The VTS and the framework
will not try to 'mmap' that initial FD.

Bug: 274456992
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I6d5783b3108886ff5c1328ddc60c623d4290d3d3