usbdevfs: move compat_ioctl handling to devio.c

Half the compat_ioctl handling is in devio.c, the other
half is in fs/compat_ioctl.c. This moves everything into
one place for consistency.

As a positive side-effect, push down the BKL into the
ioctl methods.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <oliver@neukum.org>
Cc: Alon Bar-Lev <alon.barlev@gmail.com>
Cc: David Vrabel <david.vrabel@csr.com>
Cc: linux-usb@vger.kernel.org