audio: Refactor Mmap buffer creation and handling

Unify handling of MQ and Mmap-based buffers in StreamContext.
Update 'Module::createMmapBuffer' to be called before
creating 'StreamContext'.

Flag: EXEMPT refactor
Bug: 274456992
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I8ba775360643666aa7242c673dfc10c0c817994d
Merged-In: I8ba775360643666aa7242c673dfc10c0c817994d
4 files changed