Fix/suppress bootanimation google-explicit-constructor warnings

* Add explicit to conversion constructors/operators

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: Ia6ada49250973d507ae8b10d8f0d7c2d47ee805c

cmds/bootanimation/BootAnimation.h

@@ -113,7 +113,7 @@ public:
         virtual void shutdown() {}
     };
 
-    BootAnimation(sp<Callbacks> callbacks);
+    explicit BootAnimation(sp<Callbacks> callbacks);
 
     sp<SurfaceComposerClient> session() const;
 
@@ -127,7 +127,7 @@ private:
 
     class TimeCheckThread : public Thread {
     public:
-        TimeCheckThread(BootAnimation* bootAnimation);
+        explicit TimeCheckThread(BootAnimation* bootAnimation);
         virtual ~TimeCheckThread();
     private:
         virtual status_t    readyToRun();