Fix for missing XRSettings class on Vita

Vita doesn't have XRSettings  so use the shim same as for XBoxOne and Switch

Author: PaulDunning

PostProcessing/Runtime/Utils/XRSettings.cs

@@ -1,5 +1,5 @@
-// Small shim for VRSettings/XRSettings on XboxOne and Switch
-#if (UNITY_XBOXONE || UNITY_SWITCH) && !UNITY_EDITOR
+// Small shim for VRSettings/XRSettings on XboxOne, Switch and PS Vita
+#if (UNITY_XBOXONE || UNITY_SWITCH || UNITY_PSP2) && !UNITY_EDITOR
 using System;
 
 #if UNITY_2017_2_OR_NEWER