[HLSCodeGen] increase AP_INT_MAX_W to 4096 by default

src/finn/custom_op/fpgadataflow/templates.py

 # template for single node execution
 docompute_template = """
+#define AP_INT_MAX_W 4096
 #include "cnpy.h"
 #include "npy2apintstream.hpp"
 #include <vector>
@@ -30,6 +31,7 @@ $SAVEASCNPY$
 
 # cpp file
 ipgen_template = """
+#define AP_INT_MAX_W 4096
 #include "bnn-library.h"
 // includes for network parameters
 $GLOBALS$