Documentation: devicetree: arizona: Add bindings for WM8280

Signed-off-by: Richard Fitzgerald <[e-mail]>
Signed-off-by: Charles Keepax <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/arizona.txt

···
   - compatible : One of the following chip-specific strings:
         "wlf,wm5102"
         "wlf,wm5110"
+        "wlf,wm8280"
         "wlf,wm8997"
   - reg : I2C slave address when connected using I2C, chip select number when
     using SPI.
···
   - #gpio-cells : Must be 2. The first cell is the pin number and the
     second cell is used to specify optional parameters (currently unused).
 
-  - AVDD-supply, DBVDD1-supply, DBVDD2-supply, DBVDD3-supply (wm5102, wm5110),
-    CPVDD-supply, SPKVDDL-supply (wm5102, wm5110), SPKVDDR-supply (wm5102,
-    wm5110), SPKVDD-supply (wm8997) : Power supplies for the device, as covered
-    in Documentation/devicetree/bindings/regulator/regulator.txt
+  - AVDD-supply, DBVDD1-supply, CPVDD-supply : Power supplies for the device,
+    as covered in Documentation/devicetree/bindings/regulator/regulator.txt
+
+  - DBVDD2-supply, DBVDD3-supply : Additional databus power supplies (wm5102,
+    wm5110, wm8280)
+
+  - SPKVDDL-supply, SPKVDDR-supply : Speaker driver power supplies (wm5102,
+    wm5110, wm8280)
+
+  - SPKVDD-supply : Speaker driver power supply (wm8997)
 
 Optional properties: