Gated the new GPU implementation behind the adpf_gpu_sf
flag. Changes below are not gated:

Changed to check if RenderEngine is used instead of
client composition as the latter doesn't always
trigger GPU composition (cache). And we should not set
the flag early in chooseCompositionStrategy, since if
HWC fails, it will get reset and still run on GPU.

Fixed PowerAdvisor::setGpuFenceTime code to truely
respect other displays' delay on start time

Bug: 284324521
Test: atest libcompositionengine_test PowerAdvisorTest
Change-Id: I498401d18d9886cda5c6e82243fe7cdad46e091f