Fix clang-tidy warnings in audio and playerservice.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
Test: build with WITH_TIDY=1

Change-Id: I265f3b094e08d5705b506b3fbba51439c134af84
diff --git a/media/libmediaplayerservice/HDCP.h b/media/libmediaplayerservice/HDCP.h
index 26ddc86..83c61b5 100644
--- a/media/libmediaplayerservice/HDCP.h
+++ b/media/libmediaplayerservice/HDCP.h
@@ -24,7 +24,7 @@
 namespace android {
 
 struct HDCP : public BnHDCP {
-    HDCP(bool createEncryptionModule);
+    explicit HDCP(bool createEncryptionModule);
     virtual ~HDCP();
 
     virtual status_t setObserver(const sp<IHDCPObserver> &observer);