audiohal: Pass thread identifiers to the client for priority adjustment

HALs are prohibited from using framework binder, and there is
no equivalent scheduling policy service in hwbinder. Thus, in order
to match priorities of FastCapture / Mixer threads with their
counterparts in the HAL, it is needed to request the priority boost
from audioflinger on behalf of the HAL.

Bug: 34131400
Change-Id: I7c8db9d520b4cf272d2896ad875752b109b57ab7
Test: check priority match between audioflinger's and hal's threads