Fix google-explicit-constructor warnings in audioflinger, audiopolicy.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I3b73f0cd73f47be7735cc374306c02301c20588f
diff --git a/services/audioflinger/AutoPark.h b/services/audioflinger/AutoPark.h
index e539e47..9ac7b65 100644
--- a/services/audioflinger/AutoPark.h
+++ b/services/audioflinger/AutoPark.h
@@ -21,7 +21,7 @@
 public:
 
     // Park the specific FastThread, which can be nullptr, in hot idle if not currently idling
-    AutoPark(const sp<T>& fastThread) : mFastThread(fastThread)
+    explicit AutoPark(const sp<T>& fastThread) : mFastThread(fastThread)
     {
         mPreviousCommand = FastThreadState::HOT_IDLE;
         if (fastThread != nullptr) {