Include linux/pagemap.h for release_pages and page_cache_release.

Fixes compilation error in arch/cris/mm/init.c when CONFIG_SWAP is unset.
Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Mikael Starvik <mikael.starvik@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>