staging: comedi: pcmmio: setup irq routing during (*attach)

To use interrupts the IRQ routing must be configured and interrupts
enabled. Currently both steps are being handled in pcmmio_start_intr().

Move the code that sets the IRQ routing into the attach of the board.
At this point interrupts are still disabled. The enable and polarity
bits just need to be set in pcmmio_start_intr() to enable them.

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>