Adding a power hint for face unlock.
During Tuscany runs, the Camera HAL is requesting a CAMERA_LAUNCH power
hint, which runs big and small CPU clusters at FMAX for 1 second. This is
overkill for Tuscany, so we are requesting that the hint be removed.
Tuscany should only boost during the computationally expensive image
processing, and should stop boosting as soon as a decision is reached.
This CL adds a new power hint for Tuscany. The other CLs in this topic
use this hint to boost CPU frequency during the critical section of
Tuscany by adding a call from the FaceHAL to the PowerHAL.
Running camera open and camera close without CAMERA_LAUNCH hint saves a
measured ~1W of power. The common case for this boost in Tuscany will be
a few frames at ~60ms per frame, so much less than 1 second of boost.
The worst case scenario is falsing - no attempted unlock. We will allow
the hint to time out after 1 second in that case, but that case is less
Measured latency improvement per-frame from running the CPU at FMAX is
~15ms per frame. Power measurements can be found at go/tuscany-power.
NOTE: This change will _reduce_ the power/battery impact of Tuscany by
boosting for a more precise window of time.
Test: E2E testing, validating frequency in systrace.
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