Implement some methods in 2.1 default implementation

Test: atest VtsHalGnssV2_0TargetTest builds and runs
Bug: 146216289
Change-Id: I8b024bff5b04b97298813293e39ee865eaf389b4
diff --git a/gnss/2.1/default/Gnss.h b/gnss/2.1/default/Gnss.h
index 674b070..7917bbd 100644
--- a/gnss/2.1/default/Gnss.h
+++ b/gnss/2.1/default/Gnss.h
@@ -95,6 +95,7 @@
     void reportSvStatus(const hidl_vec<GnssSvInfo>&) const;
 
     static sp<V2_1::IGnssCallback> sGnssCallback_2_1;
+    static sp<V2_0::IGnssCallback> sGnssCallback_2_0;
     std::atomic<long> mMinIntervalMs;
     sp<GnssConfiguration> mGnssConfiguration;
     std::atomic<bool> mIsActive;