Input: rotary-encoder - update docs according to the latest API changes

The old device property API is about to be removed, so
explaing how to use complete software nodes instead.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20210304090948.27014-1-heikki.krogerus@linux.intel.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/input/devices/rotary-encoder.rst

@@ -107,13 +107,17 @@ example below:
 		},
 	};
 
-	static const struct property_entry rotary_encoder_properties[] __initconst = {
+	static const struct property_entry rotary_encoder_properties[] = {
 		PROPERTY_ENTRY_U32("rotary-encoder,steps-per-period", 24),
 		PROPERTY_ENTRY_U32("linux,axis",		      ABS_X),
 		PROPERTY_ENTRY_U32("rotary-encoder,relative_axis",    0),
 		{ },
 	};
 
+	static const struct software_node rotary_encoder_node = {
+		.properties = rotary_encoder_properties,
+	};
+
 	static struct platform_device rotary_encoder_device = {
 		.name		= "rotary-encoder",
 		.id		= 0,
@@ -122,7 +126,7 @@ example below:
 	...
 
 	gpiod_add_lookup_table(&rotary_encoder_gpios);
-	device_add_properties(&rotary_encoder_device, rotary_encoder_properties);
+	device_add_software_node(&rotary_encoder_device.dev, &rotary_encoder_node);
 	platform_device_register(&rotary_encoder_device);
 
 	...