staging: comedi: addi_apci_3120: separate from addi_common.c

The addi_apci_3120 driver is the only addi-data driver that supports
dma.

Copy the code in addi_common.c to this driver and remove the #include
that caused addi_common.c to be compiled with this driver. This will
allow removing the special handling for allocating and freeing the
dma buffers in the common code.

Rename the attach_pci and detach functions so they have namespace
associated with this driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>