SF: Dedupe functions to apply Scheduler::Policy

The only functional difference is the early out when there is no change
in timer state, which now applies to LayerRequirement state as well.

Bug: 185535769
Test: libsurfaceflinger_unittest
Change-Id: Ia7234847e4f44d78dbf3920d77f38f3bfa40e5a2
6 files changed