mm: smaps: export mlock information

    Currently there is no way to find whether a process has locked its pages
    in memory or not.  And which of the memory regions are locked in memory.

    Add a new field "Locked" to export this information via the smaps file.

    Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
    Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    Acked-by: Wu Fengguang <fengguang.wu@intel.com>
    Cc: Matt Mackall <mpm@selenic.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>