dt-bindings: eeprom: at25: Add Anvo ANV32E61W

Document the compatible for ANV32E61W 64kb 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: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>