dt-bindings: iio/adc: ingenic: add the JZ4760(B) socs to the sadc Documentation

Add both the jz4760 and jz4760b, plus a property to use the internal
divider on the b variant and document it.

Signed-off-by: Christophe Branchereau <cbranchereau@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210726082033.351533-6-cbranchereau@gmail.com


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