HID: logitech-dj: allow transfer of HID++ reports from/to the correct dj device

HID++ is a Logitech-specific protocol for communicating with HID
devices. DJ devices implement HID++, and so we can add the HID++
collection in the report descriptor and forward the incoming
reports from the receiver to the appropriate DJ device.

The same can be done in the other way, if someone calls a
.raw_request(), we can forward it to the correct dj device
by overriding the device_index in the HID++ report.

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