PSP2: Force fullscreen always on

Windowed mode never worked correctly and is pointless since Vita
operating system doesn't have a window manager.

backends/platform/sdl/psp2/psp2.cpp

@@ -82,9 +82,8 @@ void OSystem_PSP2::initBackend() {
 	ConfMan.registerDefault("touchpad_mouse_mode", false);
 	ConfMan.registerDefault("frontpanel_touchpad_mode", false);
 
-	if (!ConfMan.hasKey("fullscreen")) {
-		ConfMan.setBool("fullscreen", true);
-	}
+	ConfMan.setBool("fullscreen", true);
+
 	if (!ConfMan.hasKey("aspect_ratio")) {
 		ConfMan.setBool("aspect_ratio", false);
 	}
@@ -130,6 +129,8 @@ void OSystem_PSP2::initBackend() {
 }
 
 bool OSystem_PSP2::hasFeature(Feature f) {
+	if (f == kFeatureFullscreenMode)
+		return false;
 	return (f == kFeatureKbdMouseSpeed ||
 		f == kFeatureJoystickDeadzone ||
 		f == kFeatureShader ||
@@ -142,6 +143,8 @@ void OSystem_PSP2::setFeatureState(Feature f, bool enable) {
 	case kFeatureTouchpadMode:
 		ConfMan.setBool("touchpad_mouse_mode", enable);
 		break;
+	case kFeatureFullscreenMode:
+		break;
 	default:
 		OSystem_SDL::setFeatureState(f, enable);
 		break;
@@ -153,6 +156,9 @@ bool OSystem_PSP2::getFeatureState(Feature f) {
 	case kFeatureTouchpadMode:
 		return ConfMan.getBool("touchpad_mouse_mode");
 		break;
+	case kFeatureFullscreenMode:
+		return true;
+		break;
 	default:
 		return OSystem_SDL::getFeatureState(f);
 		break;