msm: thermal: Add support to monitor only one tsens for MX restriction

Currently VDD MX restriction feature monitors all tsens for low
temperature condition. Some targets which has higher MX restriction
thresholds shows frequent interrupts from multiple sensors causing
power impact.
Add support to monitor only one sensor for VDD MX restriction feature.
Add an optional device tree property "qcom,mx-restriction-sensor_id"
to specify sensor id for monitor. If not defined, monitor all tsens
for VDD MX restriction.

Change-Id: Ib709b00c27f43c2603ac8a08b75f2fbd5800983b
Signed-off-by: Manaf Meethalavalappu Pallikunhi <manafm@codeaurora.org>