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/AudioHwDevice.cpp b/services/audioflinger/AudioHwDevice.cpp
index 12f8272..dee6161 100644
--- a/services/audioflinger/AudioHwDevice.cpp
+++ b/services/audioflinger/AudioHwDevice.cpp
@@ -110,5 +110,13 @@
     return mHwDevice->getMmapPolicyInfos(policyType, policyInfos);
 }
 
+int32_t AudioHwDevice::getAAudioMixerBurstCount() const {
+    return mHwDevice->getAAudioMixerBurstCount();
+}
+
+int32_t AudioHwDevice::getAAudioHardwareBurstMinUsec() const {
+    return mHwDevice->getAAudioHardwareBurstMinUsec();
+}
+
 
 }; // namespace android