arch-arm: Add isValid method to the TlbEntry

Change-Id: I93b183ad0768e8afc94bb3f21387c21cdc9cc78b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/arm/pagetable.hh

@@ -361,6 +361,9 @@ struct TlbEntry : public ReplaceableEntry, Serializable
     /** Need for compliance with the AssociativeCache interface */
     void insert(const Lookup &lookup) {}
 
+    /** Need for compliance with the AssociativeCache interface */
+    bool isValid() const { return valid; }
+
     void
     updateVaddr(Addr new_vaddr)
     {