Audio VTS: Enforce policy configuration format

Validate the audio_policy_configuration.xml supplied in /vendor against
the format schema.

Test: Run the VTS test on target
Test: vts-tradefed run commandAndExit vts --skip-all-system-status-check --primary-abi-only --skip-preconditions --module VtsHalAudioV2_0Target -t CheckConfig.audioPolicyConfigurationValidation
Bug: 35700978
Change-Id: I800e692a6ff4f64655007c33af7e34d879ee1132
Signed-off-by: Kevin Rocard <krocard@google.com>