Audio policy config: allow vendor to extend module name

Vendor are currently not allowed to extend the XML format.
As some enumeration are allowed to be extended, this mean that
the format must allow some extension mechanism.

This patch relaxes the definition of the module name field.
AOSP names are still allowed, but a vendor can add its own name
if prefixed with "vx_". Eg:
    <module name="vx_google_vr" halVersion="3.0">

Test: xmllint --xinclude --noout --schema hardware/interfaces/audio/2.0/config/audio_policy_configuration.xsd audio_policy_configuration.xml
      with audio_policy_configuration.xml containing a module named vx_google_vr
Test: vts-tradefed run commandAndExit vts --module VtsHalAudioV2_0Target -t CheckConfig.audioPolicyConfigurationValidation
      on Pixel 2
Bug: 69442986
Signed-off-by: Kevin Rocard <krocard@google.com>

Change-Id: I4ead38535cce89bb8fe44cf23fa1146acd1271d6