NV: Expose the nvdisp_disp0 device and a weak reference to the nvdrv:a service.

NVFlinger will call into the nvdisp_disp0 device to perform screen flips, bypassing the ioctl interface.

We now have the address of the framebuffer to draw, we just need to actually put it on the screen.

src/core/hle/service/nvdrv/nvdrv.cpp

@@ -8,9 +8,13 @@
 namespace Service {
 namespace NVDRV {
 
+std::weak_ptr<NVDRV_A> nvdrv_a;
+
 void InstallInterfaces(SM::ServiceManager& service_manager) {
-    std::make_shared<NVDRV_A>()->InstallAsService(service_manager);
+    auto nvdrv = std::make_shared<NVDRV_A>();
+    nvdrv->InstallAsService(service_manager);
+    nvdrv_a = nvdrv;
 }
 
-} // namespace nvdrv
+} // namespace NVDRV
 } // namespace Service