service/audctl: Implement GetTargetVolumeMin() and GetTargetVolumeMax()

These two service functions are literally hardcoded to always return
these values without any other error checking.

src/core/hle/service/audio/audctl.h

@@ -12,6 +12,10 @@ class AudCtl final : public ServiceFramework<AudCtl> {
 public:
     explicit AudCtl();
     ~AudCtl() override;
+
+private:
+    void GetTargetVolumeMin(Kernel::HLERequestContext& ctx);
+    void GetTargetVolumeMax(Kernel::HLERequestContext& ctx);
 };
 
 } // namespace Service::Audio