dt-bindings: eeprom: at25: Add Anvo ANV32C81W

Document the compatible for ANV32C81W 256kb Serial SPI non-volatile SRAM.
Although it is a SRAM device, it can be accessed through EEPROM interface.
At least until there is no proper SRAM driver support for it.

Signed-off-by: Marek Vasut <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/eeprom/at25.yaml

···
     oneOf:
       - items:
           - enum:
+              - anvo,anv32c81w
               - anvo,anv32e61w
               - atmel,at25256B
               - fujitsu,mb85rs1mt