iio: adc: qcom-spmi-rradc: introduce round robin adc

iio: adc: qcom-spmi-rradc: introduce round robin adc

The Round Robin ADC is responsible for reading data about the rate of
charge from the USB or DC input ports, it can also read the battery
ID (resistence), skin temperature and the die temperature of the pmic.
It is found on the PMI8998 and PM660 Qualcomm PMICs.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Link: https://lore.kernel.org/r/20220429220904.137297-6-caleb.connolly@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>