HID: core: add "report" hook, called once the report has been parsed

This callback is called when the parsing of the report has been done
by hid-core (so after the calls to .event). The hid drivers can now
have access to the whole report by relying on the values stored in
the different fields.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>