dt-bindings: iio: adc: Add AST2700 ADC compatible strings

dt-bindings: iio: adc: Add AST2700 ADC compatible strings

Add the compatible strings "aspeed,ast2700-adc0" and "aspeed,ast2700-adc1"
to the binding for the Aspeed ADC. These new compatibles represent the
ADC instances found on the AST2700 SoC, which are similar to the AST2600
but have their trimming data located at different SCU offset.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>