HID: Introduce hidpp, a module to handle Logitech hid++ devices

Logitech devices use a vendor protocol to communicate various
information with the device. This protocol is called HID++,
and an exerpt can be found here:
https://drive.google.com/folderview?id=0BxbRzx7vEV7eWmgwazJ3NUFfQ28&usp=shar



The main difficulty which is related to this protocol is that
it is a synchronous protocol using the input reports.
So when we want to get some information from the device, we need
to wait for a matching input report.

This driver introduce this capabilities to be able to support
the multitouch mode of the Logitech Wireless Touchpad T651
(the bluetooth one). The multitouch data is available directly
from the mouse input reports, and we just need to query the device
on connect about its caracteristics.

HID++ and the touchpad features has a specific reporting mode
which uses pure HID++ reports, but Logitech told us not to use
it for this specific device. During QA, they detected that
some bluetooth input reports where lost, and so the only supported
mode is the pointer mode.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>