Fix clang-tidy warnings in drm.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Idf1c48d7bfe3f0da20401cb3ff1983ec00be170d
diff --git a/drm/libdrmframework/include/IDrmManagerService.h b/drm/libdrmframework/include/IDrmManagerService.h
index fe55650..0376b49 100644
--- a/drm/libdrmframework/include/IDrmManagerService.h
+++ b/drm/libdrmframework/include/IDrmManagerService.h
@@ -169,7 +169,7 @@
 class BpDrmManagerService: public BpInterface<IDrmManagerService>
 {
 public:
-    BpDrmManagerService(const sp<IBinder>& impl)
+    explicit BpDrmManagerService(const sp<IBinder>& impl)
             : BpInterface<IDrmManagerService>(impl) {}
 
     virtual int addUniqueId(bool isNative);