mm/vmstat.c: uninline node_page_state()

mm/vmstat.c: uninline node_page_state()

With x86_64 (config http://ozlabs.org/~akpm/config-akpm2.txt) and old gcc
(4.4.4), drivers/base/node.c:node_read_meminfo() is using 2344 bytes of
stack.  Uninlining node_page_state() reduces this to 440 bytes.

The stack consumption issue is fixed by newer gcc (4.8.4) however with
that compiler this patch reduces the node.o text size from 7314 bytes to
4578.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>