PowerAdvisor: Wait for boot finished

Adds a call to PowerAdvisor so it can gate calls to
notifyDisplayUpdateImminent until the boot has finished. This prevents
PowerAdvisor from attempting to connect to the Power HAL, which can
delay the boot animation if SF comes up first.

Bug: 152131148
Test: libsurfaceflinger_unittest
Test: libcompositionengine_test
Test: Manual, check that boot is not delayed
Change-Id: Idf59e9bb62a03360925aa06d95a7b4caea36be83