mm/page_alloc: move freepage counting logic to __free_one_page()

All the caller of __free_one_page() has similar freepage counting logic,
so we can move it to __free_one_page(). This reduce line of code and help
future maintenance. This is also preparation step for "mm/page_alloc:
restrict max order of merging on isolated pageblock" which fix the
freepage counting problem on freepage with more than pageblock order.

Cc: <stable@vger.kernel.org>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Patch-mainline: linux-kernel @ 10/31/2014 16:25:29
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
CRs-fixed: 720761
Change-Id: I255d530a502f64f4c8bd1e77d5ca8cf815cdde1a