xform: now works with "arbitrary" memory sizes

Signed-off-by: Sean Cross <sean@xobs.io>

memtest/memtest.v

@@ -11,7 +11,7 @@ module memtest (
     input clki
 );
 
-    reg [31:0] mem[0:2047];
+    reg [31:0] mem[0:511];
     reg [10:0] memadr;
     assign random_rom_dat_r = mem[memadr];