dt-bindings: eeprom: at24: Add compatible for Giantec GT24C256C

dt-bindings: eeprom: at24: Add compatible for Giantec GT24C256C

The gt24c256c is another 24c256 compatible EEPROM, and does not
follow the generic name matching, so add a separate compatible for it.
This ensures accurate device-tree representation and enables proper
kernel support for systems using this part.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Wasim Nazir <wasim.nazir@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250908-lemans-evk-bu-v4-5-5c319c696a7d@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>