Thermal estimator driver.

Required properties:
 - compatible:	"nvidia,tegra124-therm-est".
 - toffset:	Temperature offset for thermal estimation, in milli-celsius.
 - polling-period: Polling wait times for thermal estimation, in milliseconds.
 - tc1:		Coefficient 1 for thermal trend calculation.
 - tc2:		Coefficient 2 for thermal trend calculation.
 - node for subdev: Node for subdevice information.

Properties in subdevice node:
 - dev: device node of the thermal zone device for thermal estimation.
 - coeffs : An array of coefficients, the number of entries should be twenty.

Example:
	skin_temp: therm-est {
		compatible = "nvidia,tegra124-therm-est";
		toffset = <9793>;
		tc1 = <10>;
		tc2 = <1>;
		polling-period = <1100>;

		#thermal-sensor-cells = <0>;

		sub-devs {
			dev@0 {
				dev = <&diode>;
				coeffs = "2 1 1 1 1 1 1 1 1 1 1 0 1 1 0 0 0 0 -1 -7";
			};

			dev@1 {
				dev = <&board>;
				coeffs = "-11 -7 -5 -3 -3 -2 -1 0 0 0 1 1 1 2 2 3 4 6 11 18";
			};
		};
	};