iio: adc: Convert the QCOM SPMI ADC bindings to .yaml format

Convert the adc bindings from .txt to .yaml format.

Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>