HID: support for Kensington slimblade device

0x47d/0x2041 device sends two extra buttons in 0xff00 usage
page and therefore requires special handling.

Reported-by: Jason Noble <nobleja@polezero.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index 9cc662c..c16fc4f 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -150,6 +150,13 @@
 	---help---
 	Support for Gyration remote control.
 
+config HID_KENSINGTON
+	tristate "Kensington" if EMBEDDED
+	depends on USB_HID
+	default !EMBEDDED
+	---help---
+	Support for Kensington Slimblade Trackball.
+
 config HID_LOGITECH
 	tristate "Logitech" if EMBEDDED
 	depends on USB_HID