staging: comedi: ni_labpc_isadma: introduce labpc_isadma_program()

Introduce a helper function to program the ISA DMA controller. Program
the ISA DMA as described in Documentation/DMA-ISA-LPC.txt.

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>