dt-bindings: iio: adc: Add Allwinner D1/T113s/R329/T507 SoCs GPADC

Allwinner's D1/T113s/R329/T507 SoCs have a new general purpose ADC.
This ADC is the same for all of this SoCs. The only difference is
the number of available channels.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Maksim Kiselev <bigunclemax@gmail.com>
Link: https://lore.kernel.org/r/20230619154252.3951913-4-bigunclemax@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>