[U-Boot] m28evk: OOT build leaves stale file in source dir

[Marek Vasut]

> Dear Marek,
> 
> when building "m28evk" out of tree, a file
> "board/denx/m28evk/memsize.c" gets created in the source directory,
> which will also not be removed by a "make mrproper" in the source
> directory.
> 
> Can you please provide a fix?

I'm on it!

> 
> Thanks in advance.

I already have fix ready :)

> 
> Best regards,
> 
> Wolfgang Denk

M