Effects: Add atomic_wp<T>, update setThread.

atomic_wp<T> is used to allow concurrent read and write to the wp<>.
We use this to fix EffectCallback::setThread to resolve multithreaded
access to the wp<T>.

Note that setThread is used for EffectChain migration between
PlaybackThreads; we also need to refine higher level transactional
locking to ensure enable/disable of effect is done consistently
during migration.

Test: basic audio works
Test: atest media_synchronization_tests
Test: AudioEffectTest AudioPreProcessingTest BassBoostTest
Test: EnvReverbTest EqualizerTest LoudnessEnhancerTest
Test: PresetReverbTest VirtualizerTest VisualizerTest
Bug: 161341295
Change-Id: If80ee4373859c832d6fd10fec0385d69064f50c6
diff --git a/media/utils/Android.bp b/media/utils/Android.bp
index e3f1e44..952fe37 100644
--- a/media/utils/Android.bp
+++ b/media/utils/Android.bp
@@ -60,3 +60,10 @@
     local_include_dirs: ["include"],
     export_include_dirs: ["include"],
 }
+
+cc_library_headers {
+    name: "libmediautils_headers",
+    vendor_available: true,  // required for platform/hardware/interfaces
+
+    export_include_dirs: ["include"],
+}