Introduces a __mod_page_state(offset, delta) function and converts
mod_page_state() to use it.

Unexports and staticizes page_states per cpu variable.

   text    data     bss     dec     hex filename
1818704  615884       0 2434588  25261c vmlinux-old
1817632  615884       0 2433516  2521ec vmlinux-new

1072 bytes. (Adds 64 bytes without CONFIG_SMP).
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>