Audio policy config: Device port (type,address) must be unique

Device port are not identified by names but by their type and address
and the module they are in.

As a result, enforce this constraint in the XSD. Violating it results in
a policy parsing crash.

Bug: 69442986
Test: xmllint invalidates an XML with two devices of the same type
      and address
Test: vts-tradefed run commandAndExit vts --module VtsHalAudioV2_0Target -t CheckConfig.audioPolicyConfigurationValidation
Change-Id: I84245f0fa80fef786a002c98073c166b6aaf2be4
Signed-off-by: Kevin Rocard <krocard@google.com>