sort out the flush_icache_range mess

[Christoph Hellwig]

On Mon, May 11, 2020 at 05:25:45PM +0200, Geert Uytterhoeven wrote:
> > Do you want to drop the:
> >
> >     select HAVE_AOUT if MMU
> >
> > for m68k then?
> 
> If that helps to reduce maintenance, it's fine for me.
> That leaves alpha as the sole user?

Yes.  And for alpha it isn't classic Linux a.out, but the OSF/1 ECOFF
format, which might lead to further cleanups eventually.