Allow NN HAL to mmap client-provided fd by default

Currently all NN services include this, so making it a default will
reduce NN service configuration.

Change-Id: I18531e57a7069076a208aefac4a545ba6c4379b0
Fixes: 120283437
Test: mma
Test: NeuralNetworksTest_static
Test: VtsHalNeuralnetworksV1_*TargetTest