lab-04: gate level model for 32-bit signed multiplier

Gate level implementation for the following components:
- MULT32_U
- MULT32
- MUX32_2x1

TESTBENCH/mult_tb.v

@@ -36,6 +36,8 @@ A=10; B=20;     // Y = 10 * 20 = 200
 #1 result[i] = {HI,LO}; i=i+1;
 #1 A=10; B=19; 	// Y = 10 * 19 = 190
 #1 result[i] = {HI,LO}; i=i+1;
+#1 A=32'h00d96027; B=32'h7c32b43c; 	// Y = 0x0d96027 * 0x7c32b43c = 0x 006975a0 b62bf524
+#1 result[i] = {HI,LO}; i=i+1;
 #1 A=32'h70000000; B=32'h70000000; 
 #1 result[i] = {HI,LO}; i=i+1;
 #1