staging: comedi: addi_apci_1500: separate from addi_common.h

Remove the need to include addi_common.h by introducing a new private
data definition. Only include the members that are actually used by
the driver.

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>