Add voltage notifier, no need to query regulator voltage for
every saradc read, just get regulator voltage once at probe.
Signed-off-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: Simon Xue <xxm@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210810011007.54066-1-xxm@rock-chips.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>