power: Add DPF and update imminent hints to AIDL

Adds FIXED_PERFORMANCE mode for the dynamic performance framework as
well as a "display update imminent hint" to the AIDL version of the
Power HAL.

Test: VtsHalPowerTargetTest
Bug: 120610745
Bug: 136285293
Bug: 146453294
Change-Id: I0cda99822eed015131f8f068512842a388f9c25c