Align default implementation with latest VSR.

VSR requires to support power HAL V2 and beyond, this patch changes the
default implementation to reflect that.

Bug: b/253516147
Test: atest VtsHalPowerTargetTest
Change-Id: I56f6f847f4c47775db6350b8a3fcd7ee9c9cdf17
diff --git a/power/aidl/default/Power.h b/power/aidl/default/Power.h
index ef6439d..7f8405e 100644
--- a/power/aidl/default/Power.h
+++ b/power/aidl/default/Power.h
@@ -26,6 +26,7 @@
 namespace example {
 
 class Power : public BnPower {
+  public:
     ndk::ScopedAStatus setMode(Mode type, bool enabled) override;
     ndk::ScopedAStatus isModeSupported(Mode type, bool* _aidl_return) override;
     ndk::ScopedAStatus setBoost(Boost type, int32_t durationMs) override;
@@ -35,6 +36,9 @@
                                          int64_t durationNanos,
                                          std::shared_ptr<IPowerHintSession>* _aidl_return) override;
     ndk::ScopedAStatus getHintSessionPreferredRate(int64_t* outNanoseconds) override;
+
+  private:
+    std::vector<std::shared_ptr<IPowerHintSession>> mPowerHintSessions;
 };
 
 }  // namespace example