Refactor adpf cpu hints to use TimePoint and Duration

Replace nsecs_t in adpf cpu hint sessions in PowerAdvisor with new
TimePoints and Durations

Additionally, added TimePoint::now() to make getting current time
cleaner

Bug: b/244358432
Test: atest libsurfaceflinger_unittest
Change-Id: I8b4d6f3de8204aa34cd9d8687febfde580deea92
10 files changed