Audio Policy: enable surround sound configuration in xml

The surround sound configuration used to be disabled. This patch
enables it, and moves out the surround sound configuration into
a dedicated file.

Bug: 116356348
Test: xmllint --noout --xinclude --schema \
      hardware/interfaces/audio/5.0/config/audio_policy_configuration.xsd \
      frameworks/av/services/audiopolicy/config/audio_policy_configuration.xml

Change-Id: I26eb55b818d813494fc31812d00e33851b79f02b