m68knommu: use asm-generic/cacheflush.h

m68knommu needs almost no cache flushing routines of its own.  Rely on
asm-generic/cacheflush.h for the defaults.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Link: http://lkml.kernel.org/r/20200515143646.3857579-15-hch@lst.de


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>