mfd: arizona: Add device tree binding documentation for new clock driver

Specify the device tree binding for the input clocks to Arizona devices.

Signed-off-by: Charles Keepax <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/arizona.txt

···
 
   - wlf,reset : GPIO specifier for the GPIO controlling /RESET
 
+  - clocks: Should reference the clocks supplied on MCLK1 and MCLK2
+  - clock-names: Should contains two strings:
+      "mclk1" for the clock supplied on MCLK1, recommended to be a high
+      quality audio reference clock
+      "mclk2" for the clock supplied on MCLK2, recommended to be an always on
+      32k clock
+
   - wlf,gpio-defaults : A list of GPIO configuration register values. Defines
     for the appropriate values can found in <dt-bindings/mfd/arizona.txt>. If
     absent, no configuration of these registers is performed. If any entry has