comedi: comedi_8255: Conditionally remove I/O port support

comedi: comedi_8255: Conditionally remove I/O port support

In a future patch, the port I/O functions (`inb()`, `outb()`, and
friends will only be declared in the `HAS_IOPORT` configuration option
is enabled.

The comedi_8255 module supports both port I/O and memory-mapped I/O.

Conditionally compile the parts of the module that use port I/O if and
only if the `CONFIG_HAS_IOPORT` macro is defined so that it can still be
built if the port I/O functions have not been declared.  If the
`CONFIG_HAS_IOPORT` macro is undefined, replace the GPL-exported
`subdev_8255_io_init()` function with a dummy static inline version that
just returns `-ENXIO`.

Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20230913170712.111719-8-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>