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 <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/proximity/semtech,sx9324.yaml

···
       UINT_MAX (4294967295) represents infinite. Other values
       represent 1-1/N.
 
+  semtech,cs-idle-sleep:
+    description:
+      State of CS pins during sleep mode and idle time.
+    enum:
+      - hi-z
+      - gnd
+      - vdd
+
   semtech,int-comp-resistor:
     description:
       Internal resistor setting for compensation.
···
         semtech,avg-pos-strength = <64>;
         semtech,int-comp-resistor = "lowest";
         semtech,input-precharge-resistor-ohms = <2000>;
+        semtech,cs-idle-sleep = "gnd";
       };
     };