staging: comedi: ii_pci20kc.c: tidy up the subdevice module init

Use the carrier board id to determine if a module is installed for
a given subdevice.

Consolidate the module init code into ii20k_init_module().

For aesthetic reasons, rename the subdevice functions to remove
'pci' from them.

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>