Support AAudioStream_flushFromFrame.

AAudioStream_flushFromFrame is an API to allow apps flush written data
from the given position. This is helpful when apps are doing offload
playback and want to rewrite the data that has been written but not yet
rendered.

Bug: 409798445
Test: atest AAudioTests
Test: test_flush_from_frame -f2 -c2 -r48000
Flag: com.android.media.audioserver.mmap_pcm_offload_support
Change-Id: I23183da9ee1d4c626e582b90e40a7645547e0cc0