adding fast DPI implemntation of imul and idiv

hw/dpi/util_dpi.vh

@@ -1,6 +1,9 @@
 `ifndef UTIL_DPI
 `define UTIL_DPI
 
+import "DPI-C" context function void dpi_imul(input int a, input int b, input logic is_signed_a, input logic is_signed_b, output int resultl, output int resulth);
+import "DPI-C" context function void dpi_idiv(input int a, input int b, input logic is_signed, output int quotient, output int remainder);
+
 import "DPI-C" context function int dpi_register();
 import "DPI-C" context function void dpi_assert(int inst, input logic cond, input int delay);