Complete TunerDescrambler aidl interface and implementation

Test: make
Bug: 159067322
Change-Id: I84322f8597080643ad5bbb829eb92f3dcd1493db
diff --git a/services/tuner/TunerDemux.h b/services/tuner/TunerDemux.h
index 9f294c6..2a9836b 100644
--- a/services/tuner/TunerDemux.h
+++ b/services/tuner/TunerDemux.h
@@ -56,6 +56,8 @@
     Status disconnectCiCam() override;
     Status close() override;
 
+    int getId() { return mDemuxId; }
+
 private:
     sp<IDemux> mDemux;
     int mDemuxId;