Input: add driver for slidebar on Lenovo IdeaPad laptops

This driver adds support for slidebars found on some Lenovo IdeaPad
laptops (the slidebars work with SlideNav/Desktop Navigator under
Windows).

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=16004

Registers 'IdeaPad Slidebar' input device and
/sys/devices/platform/ideapad_slidebar/slidebar_mode
for switching slidebar's modes.

Now works on:
IdeaPad Y550, Y550P.

May work on (testing and adding new models is needed):
Ideapad Y560, Y460, Y450, Y650,
and, probably, some others.

Signed-off-by: Andrey Moiseev <o2g.org.ru@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/Kconfig

@@ -647,4 +647,14 @@ config INPUT_SIRFSOC_ONKEY
 
 	  If unsure, say N.
 
+config INPUT_IDEAPAD_SLIDEBAR
+	tristate "IdeaPad Laptop Slidebar"
+	depends on INPUT
+	depends on SERIO_I8042
+	help
+	  Say Y here if you have an IdeaPad laptop with a slidebar.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ideapad_slidebar.
+
 endif