Add multiplier

Add 16x16 multiplier.

Pretty simple. Address 0-1 is multipled by address 2-3 and the result is
in address 4-7, all little endian of course.

hw/efinix_fpga/multiplier.sv

@@ -0,0 +1,46 @@
+module multiplier(
+    input clk,
+    input reset,
+    input [7:0] i_data,
+    output logic [7:0] o_data,
+    input cs,
+    input rwb,
+    input [2:0] addr
+);
+
+logic [15:0] a, b;
+logic [31:0] out;
+
+always_ff @(negedge clk) begin
+    if (reset) begin
+        a <= '0;
+        b <= '0;
+    end
+
+
+    if (cs & ~rwb) begin
+        case (addr)
+            3'h0: begin
+                a[7:0] <= i_data;
+            end
+
+            3'h1: begin
+                a[15:8] <= i_data;
+            end
+
+            3'h2: begin
+                b[7:0] <= i_data;
+            end
+
+            3'h3: begin
+                b[15:8] <= i_data;
+            end
+        endcase
+    end
+end
+
+assign out = a * b;
+assign o_data = out[((addr-4)*8)+:8];
+
+
+endmodule