staging: comedi: addi_apci_3120: fix timer (*insn_config)

The timer subdevice in this driver does not follow the comedi API.

Fix the (*insn_config) to correctly arm, disarm, set the mode, and
get the status of the timer.

Remove the unnecessary, and broken, (*insn_write).

The new (*insn_config) does not enable the interrupt for timer 2.
Remove the interrupt support code for the timer.

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>