HID: Scan the device for group info before adding it

In order to allow the report descriptor to influence the hid device
properties, one needs to parse the descriptor early, without reference
to any driver. Scan the descriptor for group information during device
add, before the device has been broadcast to userland. The device
modalias will contain group information which can be used to
differentiate between modules. For starters, just handle the generic
group.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Acked-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>