nvflinger: Implement swap intervals

src/core/hle/service/nvflinger/nvflinger.h

@@ -74,6 +74,8 @@ public:
     /// finished.
     void Compose();
 
+    s64 GetNextTicks();
+
 private:
     /// Finds the display identified by the specified ID.
     VI::Display* FindDisplay(u64 display_id);
@@ -98,6 +100,8 @@ private:
     /// layers.
     u32 next_buffer_queue_id = 1;
 
+    u32 swap_interval = 1;
+
     /// Event that handles screen composition.
     Core::Timing::EventType* composition_event;