Use customized event flag for data FMQ not_empty to avoid conflict

Bug: 335547630
Test: atest --test-mapping hardware/interfaces/audio/aidl/vts:presubmit
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f174d1ed60fe574540013043024d02ebae4f6fe2)
Merged-In: I0f5776edd58748195df61e4dae911df30f40e5b0
Change-Id: I0f5776edd58748195df61e4dae911df30f40e5b0