HID: Add an input configured notification callback

A hid device may create several input devices, and a driver may need
to prepare or finalize the configuration per input device. Currently,
there is no sane way for a driver to know when a device has been
configured. This patch adds a callback providing that information.

Reviewed-and-tested-by: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Tested-by: Ping Cheng <pingc@wacom.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>