rc_input: add RC_PORT_CONFIG param to configure RC port

The parameter will only be available if the board defines an 'RC' serial
port in SERIAL_PORTS (in default.cmake).

src/drivers/rc_input/CMakeLists.txt

@@ -38,6 +38,8 @@ px4_add_module(
 	SRCS
 		RCInput.cpp
 		crsf_telemetry.cpp
+	MODULE_CONFIG
+		module.yaml
 	DEPENDS
 		rc
 	)

src/drivers/rc_input/module.yaml

@@ -0,0 +1,12 @@
+module_name: RC Input Driver
+serial_config:
+    - command: set RC_INPUT_ARGS "-d ${SERIAL_DEV}"
+      port_config_param:
+        name: RC_PORT_CONFIG
+        group: Serial
+        default: RC
+        depends_on_port: RC
+        description_extended: |
+            Setting this to 'Disabled' will use a board-specific default port
+            for RC input.
+