audio: add readMmap and writeMmap for mmap stream. am: 4b3f468e0a

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3522554

Change-Id: Ic89581b3b5d1cac1ece419ebed68bdba4d18bf84
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>