iio/adc: ingenic: add JZ4760B support to the sadc driver

iio/adc: ingenic: add JZ4760B support to the sadc driver

The JZ4760B variant differs slightly from the JZ4760: it has a bit called VBAT_SEL in the CFG register.

In order to correctly sample the battery voltage on existing handhelds using this SOC, the bit must be cleared.

We leave the possibility to set the bit, by using the "ingenic,use-internal-divider" in the devicetree.

Signed-off-by: Christophe Branchereau <cbranchereau@gmail.com>
Link: https://lore.kernel.org/r/20210726082033.351533-5-cbranchereau@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>