mips: drop _PAGE_FILE and pte_file()-related helpers

mips: drop _PAGE_FILE and pte_file()-related helpers

commit b32da82e28ce90bff4e371fc15d2816fa3175bb0 upstream.

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

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: Deleted definitions are slightly different]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>