msm: thermal: Restrict APSS frequency at low temperature.

Add support for thermal to limit the max frequency the
CPU cores can scale at low temperatures. This is an optional
feature that can be enabled based on the devicetree property
qcom,max-freq-level.

This restriction is done as a part of the existing vdd
restriction feature, which limits the floor corner level
of a voltage rail. With the optional property
"qcom,max-freq-level" defined, KTM now will restrict both
the scaling min and scaling max frequency of the CPU rail
at low temperature.

Change-Id: Ic40bc98c3ef5cba897e565f5b6b3651a9eb2f69e
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>