dt-bindings: iio: adc: mcp3911: add support for the whole MCP39xx family

dt-bindings: iio: adc: mcp3911: add support for the whole MCP39xx family

Microchip does have many similar chips, add those to the compatible
string as the driver support is extended.

The new supported chips are:
  - microchip,mcp3910
  - microchip,mcp3912
  - microchip,mcp3913
  - microchip,mcp3914
  - microchip,mcp3918
  - microchip,mcp3919

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230822192259.1125792-2-marcus.folkesson@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>