Relax NeuralNetwork's VTS positive and negative base tests

There are some NN VTS tests that assume a service is able to generate a
model consisting only of a floating point add operation. However, some
drivers do not support floating point operations. This CL relaxes the
test requirements to allow a test to be skipped if the service does not
support floating point add.

Bug: 72764145
Test: mma
Test: VtsHalNeuralnetworksV1_0TargetTest
Change-Id: I6b0644432680fc2f8098b5187795dc2953df03f9