BLAST: Two start-up optimizations

1. Avoid a seperate IPC querying in to system-server
   to initialize the mUseBLAST flag.
2. Avoid calling property_get_bool with each BufferQueue
   creation.

Instead we piggy-back both values inside addWindow return values.

Bug: 152501005
Test: Existing tests pass
Change-Id: If130560a8230f8d399cf7631264d551522939faa