dt-bindings: iio: sx9324: Add CS idle/sleep mode

dt-bindings: iio: sx9324: Add CS idle/sleep mode

We need to configure the sleep and idle mode of the CS pins for this
device. Add a DT property to do this so pins are in a proper state
during sleep (either hi-z, grounded, or pulled up to vdd).

Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220503193937.3794477-2-swboyd@chromium.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>