tmpfs: fix mempolicy object leaks

This patch fixes several mempolicy leaks in the tmpfs mount logic.
These leaks are slow - on the order of one object leaked per mount
attempt.

Leak 1 (umount doesn't free mpol allocated in mount):
    while true; do
        mount -t tmpfs -o mpol=interleave,size=100M nodev /mnt
        umount /mnt
    done

Leak 2 (errors parsing remount options will leak mpol):
    mount -t tmpfs -o size=100M nodev /mnt
    while true; do
        mount -o remount,mpol=interleave,size=x /mnt 2> /dev/null
    done
    umount /mnt

Leak 3 (multiple mpol per mount leak mpol):
    while true; do
        mount -t tmpfs -o mpol=interleave,mpol=interleave,size=100M nodev /mnt
        umount /mnt
    done

This patch fixes all of the above.  I could have broken the patch into
three pieces but is seemed easier to review as one.

Signed-off-by: Greg Thelen <gthelen@google.com>

(https://lkml.org/lkml/2013/2/20/55)
CPU hotplug, writeback: Don't call writeback_set_ratelimit() too often during hotplug

The CPU hotplug callback related to writeback calls writeback_set_ratelimit() during every state
change in the hotplug sequence. This is unnecessary since num_online_cpus() changes only once
during the entire hotplug operation.

So invoke the function only once per hotplug, thereby avoiding the unnecessary repetition
of those costly calculations.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

(https://gitorious.org/linux-ar933x-usb/linux-ar933x-usb/commit/2f60d628ffd042e65e0b1d3431fb3e38d6f7c1be)
Enable 2.0GHz CPU freq