iio: adc: Add support for the Renesas RZ/N1 ADC

iio: adc: Add support for the Renesas RZ/N1 ADC

The Renesas RZ/N1 ADC controller is the ADC controller available in the
Renesas RZ/N1 SoCs family. It can use up to two internal ADC cores (ADC1
and ADC2) those internal cores are not directly accessed but are handled
through ADC controller virtual channels.

Signed-off-by: Herve Codina (Schneider Electric) <herve.codina@bootlin.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>