Add HAL interface to replace aaudio system property.

Using the HAL interface instead of reading system property is a better
option when moving to AIDL HAL. The replaced property includes:
  - aaudio.mixer_bursts
  - aaudio.hw_burst_min_usec

Test: atest AAudioTests
Bug: 193275465
Change-Id: I9c9a04296e56ff083babcfa089fcdddc6b89ed94
diff --git a/services/audioflinger/PropertyUtils.h b/services/audioflinger/PropertyUtils.h
index 3bb6fa2..fbf651a 100644
--- a/services/audioflinger/PropertyUtils.h
+++ b/services/audioflinger/PropertyUtils.h
@@ -25,4 +25,8 @@
         media::audio::common::AudioMMapPolicyType policyType,
         std::vector<media::audio::common::AudioMMapPolicyInfo> *policyInfos);
 
+int32_t getAAudioMixerBurstCountFromSystemProperty();
+
+int32_t getAAudioHardwareBurstMinUsecFromSystemProperty();
+
 } // namespace android