libbinderthreadstateutils: don't init binder

Don't initialize binder/hwbinder thread state if they
aren't already initialized. This is fine - if we
know they aren't initialized, then there is no binder
call going.

Bug: 205282403
Test: libbinderthreadstateutils_test
TesT: binderRpcTest (because it uses these APIs in a special way)
Change-Id: Id67010bb15559e85dd764746525562acc7e1f13c