Implement ArInterruptsEnabled() routine

xtoskrnl/includes/amd64/ari.h

@@ -42,6 +42,10 @@ XTAPI
 VOID
 ArInitializeProcessor(IN PVOID ProcessorStructures);
 
+XTCDECL
+BOOLEAN
+ArInterruptsEnabled(VOID);
+
 XTCDECL
 VOID
 ArInvalidateTlbEntry(IN PVOID Address);