dt-bindings: hwmon: ti,ina2xx: Add ti,shunt-gain property

Add a property to the binding to define the selected shunt voltage gain.
This specifies the range and accuracy that applies to the shunt circuit.
This property only applies to devices that have a selectable shunt
voltage range via PGA or ADCRANGE register configuration.

Signed-off-by: Nathan Rossi <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/devicetree/bindings/hwmon/ti,ina2xx.yaml

···
       Shunt resistor value in micro-Ohm.
     $ref: /schemas/types.yaml#/definitions/uint32
 
+  ti,shunt-gain:
+    description: |
+      Programmable gain divisor for the shunt voltage accuracy and range. This
+      property only applies to devices that have configurable PGA/ADCRANGE. The
+      gain value is used configure the gain and to convert the shunt voltage,
+      current and power register values when reading measurements from the
+      device.
+
+      For devices that have a configurable PGA (e.g. INA209, INA219, INA220),
+      the gain value maps directly with the PG bits of the config register.
+
+      For devices that have ADCRANGE configuration (e.g. INA238) a shunt-gain
+      value of 1 maps to ADCRANGE=1 where no gain divisor is applied to the
+      shunt voltage, and a value of 4 maps to ADCRANGE=0 such that a wider
+      voltage range is used.
+
+      The default value is device dependent, and is defined by the reset value
+      of PGA/ADCRANGE in the respective configuration registers.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [1, 2, 4, 8]
+
 required:
   - compatible
   - reg