msm: thermal: Add cpu mask control for frequency limiting

Limit the number of cpus affected by kernel thermal module's frequency
control mechanism by specifying the participating cpus in the
freq-control-mask. Frequency control can be disabled, if the mask is 0.

Change-Id: Iab659730dd06ce59521917c8ba6210d7dd1311b0
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>