mn10300: drop _PAGE_FILE and pte_file()-related helpers

We've replaced remap_file_pages(2) implementation with emulation.  Nobody
creates non-linear mapping anymore.

This patch also increases the number of bits availble for swap offset.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>