sh: export copy-page() to modules

ERROR: "copy_page" [fs/unionfs/unionfs.ko] undefined!

like all the other architectures.

Cc: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>