staging: comedi: ni_mio_common: remove forward declaration 7

Move the programmable function inputs subdevice functions and helpers
to remove the need for the forward declarations.
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>