Updates to AudioPolicyManager refactor

Use protected access in AudioPolicyManager class for
 - engine field
 - querying phone state
 - isStrategyActive

Fix inclusion of AudioPolicyManagerInterface header.

Use "APM_" prefix in audio policy conf parsing code to avoid
 naming conflicts with some HALs.

DeviceDescriptor and its collection class are good friends now.

Change-Id: I236d62a2b8a4b6bf68dd515932650b912577c145
diff --git a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
index aa2e044..797a2b4 100644
--- a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
+++ b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
@@ -521,6 +521,10 @@
     }
 }
 
+audio_mode_t AudioPolicyManager::getPhoneState() {
+    return mEngine->getPhoneState();
+}
+
 void AudioPolicyManager::setForceUse(audio_policy_force_use_t usage,
                                          audio_policy_forced_cfg_t config)
 {