dt-bindings: at24: make wp-gpios a reference to the property defined by nvmem

NVMEM framework is an interface for the at24 EEPROMs as well as for
other drivers, instead of passing the wp-gpios over the different
drivers each time, it would be better to pass it over the NVMEM
subsystem once and for all.

Making wp-gpios a reference to the property defined by nvmem.
Signed-off-by: Khouloud Touil <ktouil@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Documentation/devicetree/bindings/eeprom/at24.yaml

@@ -145,10 +145,7 @@ properties:
       over reads to the next slave address. Please consult the manual of
       your device.
 
-  wp-gpios:
-    description:
-      GPIO to which the write-protect pin of the chip is connected.
-    maxItems: 1
+  wp-gpios: true
 
   address-width:
     allOf: