dt-bindings: at24: add new compatible

arch/arm/boot/dts/at91-dvk_som60.dt.yaml uses the compatible string
'giantec,gt24c32a' for an at24 EEPROM with a fallback to 'atmel,24c32'.

Add this model as a special case to the binding document.
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/eeprom/at24.yaml

@@ -107,6 +107,9 @@ properties:
       - items:
           - const: renesas,r1ex24016
           - const: atmel,24c16
+      - items:
+          - const: giantec,gt24c32a
+          - const: atmel,24c32
       - items:
           - const: renesas,r1ex24128
           - const: atmel,24c128