m68k/m68knommu: clean up page.h

There is a lot of common defines in the MMU and non-MMU variants of
page.h. Factor out the common stuff into the master page.h. It still
includes the underlying page_mm.h or page_no.h, but they only contain
the real differences now.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>