dt-bindings: eeprom: at25: add st,m95640 compatible

The st,m95640 is a 64 Kbit SPI eeprom in the same family as the two
existing st,m95* compatibles.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230614201056.379080-1-linux@rasmusvillemoes.dk


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