audio: add reporting of gapless playback support

Add reporting of gapless playback support via
getOffloadSupport() method which replaces isOffloadSupported().
The audio HAL implementation indicates gapless support by setting flag
AUDIO_OUTPUT_FLAG_GAPLESS_OFFLOAD on an output profile in addition to
flag AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD.

Bug: 158191844
Test: make
Change-Id: I7a8fa284c2486fd7a74782acb1ac7537d1534e49
diff --git a/services/audiopolicy/AudioPolicyInterface.h b/services/audiopolicy/AudioPolicyInterface.h
index b00426f..bbf9343 100644
--- a/services/audiopolicy/AudioPolicyInterface.h
+++ b/services/audiopolicy/AudioPolicyInterface.h
@@ -220,7 +220,7 @@
     virtual status_t    dump(int fd) = 0;
 
     virtual status_t setAllowedCapturePolicy(uid_t uid, audio_flags_mask_t flags) = 0;
-    virtual bool isOffloadSupported(const audio_offload_info_t& offloadInfo) = 0;
+    virtual audio_offload_mode_t getOffloadSupport(const audio_offload_info_t& offloadInfo) = 0;
     virtual bool isDirectOutputSupported(const audio_config_base_t& config,
                                          const audio_attributes_t& attributes) = 0;