staging: comedi: addi_apci_1564: move apci1564_di_insn_bits() to addi_apci_1564.c

This function is already compliant with the comedi API and is behaving as
comedi core expects.  This patch moves it out of
addi-data/hwdrv_apci1564.c and into the driver proper since no further
work needs to be done on it.

Signed-off-by: Chase Southwood <chase.southwood@gmail.com>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>