iio: adc: sc27xx: add support for PMIC sc2720 and sc2721

sc2720 and sc2721 is the product of sc27xx series.

Co-developed-by: Yuming Zhu <yuming.zhu1@unisoc.com>
Signed-off-by: Yuming Zhu <yuming.zhu1@unisoc.com>
Signed-off-by: Cixi Geng <cixi.geng1@unisoc.com>
Link: https://lore.kernel.org/r/20220419142458.884933-7-gengcixi@gmail.com


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