dt-bindings: eeprom: at25: add fujitsu,mb85rs256 compatible

The fujitsu,mb85rs256 is a 256 Kbit SPI memory FRAM in the same family
as the two existing fujitsu,mb85rs* compatibles and at25 compatible.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240612092934.12282-1-francesco@dolcini.it


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>