staging: comedi: ni_6527: introduce ni6527_reset()

Factor the board reset code out of the (*attach). Do the reset as
soon as possible to ensure the interrupts are disabled.

For convienence, use the ni6257_reset() during the (*detach) instead
of just disabling the interrupts.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>