[FRONTEND][BACKEND] Fixes for cat / reshape / addptr (#959)

Most notably, this PR:
- changes the traits (and assembly format) of addptr so it can handle offsets that have arbitrary integer width.
- adds support for `cat`

lib/Dialect/Triton/IR/Traits.cpp

@@ -19,7 +19,7 @@ mlir::OpTrait::impl::verifySameOperandsAndResultEncoding(Operation *op) {
   for (auto resultType : op->getResultTypes())
     if (failed(verifySameEncoding(resultType, type)))
       return op->emitOpError()
-             << "requires the same shape for all operands and results";
+             << "requires the same encoding for all operands and results";
   return verifySameOperandsEncoding(op);
 }