Add FL6 spec tests to AIDL VTS.

Also skip FL6 (AIDL_V2) tests for older AIDL drivers.

Bug: 203038813
Test: VtsHalNeuralnetworksTargetTest
Specifically, for old driver such as AIDL_V1 sample driver, it can pass
HIDL tests and skip AIDL_V2 tests. For new driver such as AIDL_V2
sample driver, it can pass all tests.

Change-Id: I689fef0945428f6548977628e3c43628dd1e5bf7