UI: Ask for restart when changing graphics device.

Only for D3D11 and Vulkan.

Also, makes Vulkan follow D3D11 in not changing the setting if the device
is not found on startup.

Core/System.cpp

@@ -97,6 +97,7 @@ volatile bool coreStatePending = false;
 static volatile CPUThreadState cpuThreadState = CPU_THREAD_NOT_RUNNING;
 
 static GPUBackend gpuBackend;
+static std::string gpuBackendDevice;
 
 void ResetUIState() {
 	globalUIState = UISTATE_MENU;
@@ -124,14 +125,19 @@ GlobalUIState GetUIState() {
 	return globalUIState;
 }
 
-void SetGPUBackend(GPUBackend type) {
+void SetGPUBackend(GPUBackend type, const std::string &device) {
 	gpuBackend = type;
+	gpuBackendDevice = device;
 }
 
 GPUBackend GetGPUBackend() {
 	return gpuBackend;
 }
 
+std::string GetGPUBackendDevice() {
+	return gpuBackendDevice;
+}
+
 bool IsAudioInitialised() {
 	return audioInitialized;
 }