This is a cleanup of hiddev and fixes the following issues:

- thread safety by locking in read & ioctl, introducing a per device mutex
- race between ioctl and disconnect, introducing a flag and locking
  in form of a per low level device mutex
- race between open and other methods, making sure only successfully
  opened devices are put on the list, changing order of events
- range checking both upper and lower limits of the minor range
- make sure further calls to open fail for unplugged devices even if
  the device still has opened files
- error checking for low level open
- possible loss of wakeup events, using standard waiting macros
- race in initialisation by moving registration after full initialisation
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>