Documentation: Add ABI doc for attributes of LJCA device

Add sysfs attributes Documentation entries for LJCA device

Signed-off-by: Ye Xiang <xiang.ye@intel.com>

Documentation/ABI/testing/sysfs-bus-usb-devices-ljca

@@ -0,0 +1,22 @@
+What:		/sys/bus/usb/.../version
+Date:		July 2023
+KernelVersion:	6.4
+Contact:	Ye Xiang <xiang.ye@intel.com>
+Description:
+		Provides the current firmware version of LJCA device.
+		The format is Major.Minor.Patch.Build, where
+		Major, Minor, Patch, and Build are decimal numbers.
+		For example: 1.0.0.256
+
+What:		/sys/bus/usb/.../cmd
+Date:		July 2023
+KernelVersion:	6.4
+Contact:	Ye Xiang <xiang.ye@intel.com>
+Description:
+		Commands supported by LJCA device.
+		When read, it will return valid commands.
+		When write with a command, it will execute the command.
+		Valid commands are [dfu, debug]
+		dfu:	Echo dfu to this file so as to put the device into
+			DFU mode so the firmware can be updated.
+		debug:	Enable debug logging.