dt-bindings: at24: Add address-width property

Currently the only way to use a variant of a supported model with
a different address width is to define a new compatible string and
the corresponding chip data structure.

Provide a flexible way to specify the size of the address pointer
by defining a new property: address-width.

Signed-off-by: Alan Chiang <alanx.chiang@intel.com>
Signed-off-by: Andy Yeh <andy.yeh@intel.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
[Bartosz: fixed the commit message]
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Documentation/devicetree/bindings/eeprom/at24.txt

@@ -72,6 +72,8 @@ Optional properties:
 
   - wp-gpios: GPIO to which the write-protect pin of the chip is connected.
 
+  - address-width: number of address bits (one of 8, 16).
+
 Example:
 
 eeprom@52 {