Merge changes from topic "cp_nnapi"

* changes:
  Relax NeuralNetwork's VTS positive and negative base tests
  Add Capabilities::relaxedFloat32toFloat16Performance for 1.1.
  Minor modification to allow relaxed precision test
  NNAPI narrow evaluation for P -- HAL
  Refactor NN API VTS tests and add v1.1 tests
  Add README to NeuralNetworks HAL