mm: Support address range reclaim

This patch adds address range reclaim of a process.
The requirement is following as,

Like webkit1, it uses a address space for handling multi tabs.
IOW, it uses *one* process model so all tabs shares address space
of the process. In such scenario, per-process reclaim is rather
coarse-grained so this patch supports more fine-grained reclaim
for being able to reclaim target address range of the process.
For reclaim target range, you should use following format.

	echo [addr] [size-byte] > /proc/pid/reclaim
The addr should be page-aligned.

So now reclaim konb's interface is following as.

echo file > /proc/pid/reclaim
	reclaim file-backed pages only
echo anon > /proc/pid/reclaim
	reclaim anonymous pages only
echo all > /proc/pid/reclaim
	reclaim all pages
echo 0x100000 8K > /proc/pid/reclaim
	reclaim pages in (0x100000 - 0x102000)

Change-Id: I111131d31be1cfcfa246617b634a9a8bc4078098
Signed-off-by: Minchan Kim <minchan@kernel.org>
Patch-mainline: linux-mm @ 9 May 2013 08:39:01
[vinmenon@codeaurora.org: trivial merge conflict fixes]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>