remove mm_{ptov,vtop}()

This patch removes the unused mm_{ptov,vtop}().

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Bryan Wu <bryan.wu@analog.com>
Cc: Miles Bader <miles.bader@necel.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>