Pumpkin Cinnamon Cream Cheese Dump Cake

cream cheese3/4 C. powdered sugar2 tsp. milk1 can (29 oz.) pumpkin puree1 can (12 oz.) evaporated milk3 eggs1 1/4 C. sugar1 tsp. salt1 Tbsp. pumpkin pie spice1 yellow cake mix (dry)1/2 C. butter, melted1 Tbsp. cinnamon sugar mixture, optionalwhipped cream