staging: comedi: conditionally build in PCI driver support

Separate the comedi_pci_* functions out of drivers.c into a new
source file, comedi_pci.c. This allows conditionally building
support for comedi PCI drivers into the comedi core. Fix the
Kconfig and Makefile appropriately.

Group all the comedi_pci_* prototypes and related defines into one
place in comedidev.h. Protect these prototypes with an #ifdef and
provide some dummy functions so that the mixed ISA/PCI comedi
drivers will still build correctly.

Remove the #include <linux/pci.h> from comedidev.h and drivers.c. This
include is only needed by the comedi PCI driver support code and the
PCI drivers. The include should occur in those files.

Also, remove the #include <linux/pci.h> from a couple non-PCI drivers
since it's not needed.

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>