mm: extract reclaim code from __alloc_pages_direct_reclaim()

This patch extracts common reclaim code from __alloc_pages_direct_reclaim()
function to separate function: __perform_reclaim() which can be later used
by alloc_contig_range().

Change-Id: Ia9d8b82018d91dc669488955b20f69f1cba43147
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Tested-by: Rob Clark <rob.clark@linaro.org>
Tested-by: Ohad Ben-Cohen <ohad@wizery.com>
Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Tested-by: Robert Nelson <robertcnelson@gmail.com>
Tested-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>