[audio] Bind TTS with FOREGROUND_SERVICE

Add BIND_FOREROUND_SERVICE to the system binding to TTSService. This
ensures that it is treated as an FGS when audio evaluates capabilities.

Test: manual Select To Speak verification
Bug: 385654000
Bug: 376481063
Flag: EXEMPT bug fix
Change-Id: I8767640c2cb9e4a8861f4a01780357f8e087a649