Add reset input to memory mapper

Upon reset the memory mapper is automatically disabled, but the mappings
are not cleared.

hw/fpga/memory_mapper.sv

@@ -7,6 +7,7 @@
 
 module memory_mapper(
 	input clk,
+	input rst,
 
 	input rw,
 	input cs,
@@ -29,6 +30,9 @@ logic MM;
 
 
 always_ff @(posedge clk) begin
+    if (rst) begin
+        MM <= '0;
+    end else begin
         if (MM_cs & ~rw) begin					// can't read MM but do you really need too?
             MM = |data_in;
         end
@@ -39,6 +43,7 @@ always_ff @(posedge clk) begin
             data_out <= RAM[RS];
         end
     end
+end
 
 
 always_comb begin

hw/fpga/super6502.sv

@@ -94,6 +94,7 @@ assign mm_address = {mm_MO, cpu_addr[11:0]};
 
 memory_mapper memory_mapper(
 	.clk(clk),
+    .rst(rst),
 	.rw(cpu_rwb),
 	.cs(mm_cs1),
 	.MM_cs(mm_cs2),