dt-bindings: trivial-devices: Add mcp342x ADCs and drop separate binding doc.

These i2c devices have simple bindings, well described by trivial-device.yaml
so rather than convert the binding doc to yaml, let us just add them to
trivial devices and drop the old binding document.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Link: https://lore.kernel.org/r/20200809111753.156236-3-jic23@kernel.org

Documentation/devicetree/bindings/iio/adc/mcp3422.txt

-* Microchip mcp3421/2/3/4/6/7/8 chip family (ADC)
-
-Required properties:
- - compatible: Should be
-	"microchip,mcp3421" or
-	"microchip,mcp3422" or
-	"microchip,mcp3423" or
-	"microchip,mcp3424" or
-	"microchip,mcp3425" or
-	"microchip,mcp3426" or
-	"microchip,mcp3427" or
-	"microchip,mcp3428"
- - reg: I2C address for the device
-
-Example:
-adc@0 {
-	compatible = "microchip,mcp3424";
-	reg = <0x68>;
-};

Documentation/devicetree/bindings/trivial-devices.yaml

@@ -128,6 +128,22 @@ properties:
           - mcube,mc3230
             # MEMSIC 2-axis 8-bit digital accelerometer
           - memsic,mxc6225
+            # Microchip differential I2C ADC, 1 Channel, 18 bit
+          - microchip,mcp3421
+            # Microchip differential I2C ADC, 2 Channel, 18 bit
+          - microchip,mcp3422
+            # Microchip differential I2C ADC, 2 Channel, 18 bit
+          - microchip,mcp3423
+            # Microchip differential I2C ADC, 4 Channel, 18 bit
+          - microchip,mcp3424
+            # Microchip differential I2C ADC, 1 Channel, 16 bit
+          - microchip,mcp3425
+            # Microchip differential I2C ADC, 2 Channel, 16 bit
+          - microchip,mcp3426
+            # Microchip differential I2C ADC, 2 Channel, 16 bit
+          - microchip,mcp3427
+            # Microchip differential I2C ADC, 4 Channel, 16 bit
+          - microchip,mcp3428
             # Microchip 7-bit Single I2C Digital POT (5k)
           - microchip,mcp4017-502
             # Microchip 7-bit Single I2C Digital POT (10k)