aaudio: fix returned performanceMode for Legacy

AAudio was setting the stream to PERFORMANCE_MODE_NONE
if we got the FAST mixer but did not get the RAW flag.
We now consider FAST flag by itself to be LOW_LATENCY.

Bug: 63004643
Test: see bug for repro case using NativeOboe app
Change-Id: Id4643d20926a8e983cd28408f70e176976c02195