stop offload only when current display state is unsupported by offload

"stop offload" was always executed which could be redundant and make
screen brightness flaky. This CL makes "stop offload" only happen when
current display state is not suitable for offload.

Test: Manual
Bug: 325156852
Change-Id: Ic80e7034e9b30a9260833e02b7713c73bb2efbcb