UsecaseValidator: ignore special use cases when usage is unknown

The game usecase validator must ignore special routing use cases
indicated by audio attributes flags (BT SCO, TTS...) when the usage
is unknown.

Also fix a problem in ToneGenerator where the attributes flags were
overwritten when the low latency flag was set.

Bug: 283014940
Test: repro steps in bug
Change-Id: I4d5a038436b0dd2453dd8320dafba478970bb06e