dt-bindings: thermal: k3: Add VTM bindings documentation

Add VTM bindings documentation. In the Voltage Thermal
Management Module(VTM), K3 AM654 supplies a voltage
reference and a temperature sensor feature that are gathered in the band
gap voltage and temperature sensor (VBGAPTS) module. The band
gap provides current and voltage reference for its internal
circuits and other analog IP blocks. The analog-to-digital
converter (ADC) produces an output value that is proportional
to the silicon temperature.

Reviewed-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>

Documentation/devicetree/bindings/thermal/ti_k3_thermal.txt

@@ -0,0 +1,29 @@
+* Texas Instrument K3 VTM bandgap bindings
+
+In the Voltage Thermal Management Module(VTM), K3 supplies a voltage
+reference and a temperature sensor feature that are gathered in the band
+gap voltage and temperature sensor (VBGAPTS) module. The band
+gap provides current and voltage reference for its internal
+circuits and other analog IP blocks. The analog-to-digital
+converter (ADC) produces an output value that is proportional
+to the silicon temperature.
+
+Required properties:
+- compatible : Should be:
+  - "ti,am654-vtm" : for K3 AM654 VTM bandgap
+- reg: Base address and address range of the VTM registers
+- power-domains  : Should contain a phandle to a PM domain provider node and an
+                   args specifier containing the VTM device id value. This
+                   property is as per the binding,
+                       Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
+- #thermal-sensor-cells: Should be 1. See ./thermal.txt for a description
+
+Example:
+
+AM654:
+wkup_vtm0: wkup_vtm0@42050000 {
+	compatible = "ti,am654-vtm";
+	reg = <0x0 0x42050000 0x0 0x25c>;
+	power-domains = <&k3_pds 80>;
+	#thermal-sensor-cells = <1>;
+};