Use libbinderthreadstateutils.

Clients needing to differentiate between system/vendor used to be able
to use isServingCall. However, this was expensive to implement. This
alternative approach instead requires users of this API to use
libbinderthreadstateutils which does a slighty different operation.

Bug: 148692216
Test: atest VtsHalCameraServiceV2_0TargetTest
Test: running AImageReaderVendorTest
Test: try face unlock
Change-Id: I5615f4e8863487d0de8dad2d0529214750897036