comedi: ni_mio_common: Conditionally use I/O port or MMIO

comedi: ni_mio_common: Conditionally use I/O port or MMIO

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 "ni_mio_common.c" file contains calls to both port I/O functions and
memory-mapped I/O functions.  The file is `#include`d by "ni_atmio.c",
"ni_mio_cs.c", and "ni_pcimio.c" for the ni_atmio, ni_mio_cs, and
ni_pcimio modules, respectively.  Only "ni_pcimio.c" defines the
`PCIDMA` macro before including "ni_mio_common.c" and various bits of
code in "ni_mio_common.c" is conditionally compiled according to whether
that macro is defined or not.  Currently, the port I/O function calls
are compiled in regardless of whether the `PCIDMA` macro is defined or
not.  However, the fact is that the ni_atmio and ni_mio_cs modules will
never call the memory-mapped I/O functions, and the ni_pcimio module
will never call the port I/O functions.

Calls to the port I/O and memory-mapped I/O functions is confined to the
`ni_writel()`, `ni_writew()`, `ni_writeb()`, `ni_readl()`, `ni_readw()`,
and `ni_readb()` functions which do a run-time test to decide whether to
call the port I/O functions or the memory-mapped I/O functions.
Conditionally compile two variants of the functions so they only call
the port I/O functions if the `PCIDMA` macro is undefined (for the
ni_atmio and ni_mio_cs modules), and only call the memory-mapped I/O
functions if the `PCIDMA` macro is defined (for the ni_pcimio module).

Add a run-time check in the `ni_E_init()` function to return an error if
the comedi device has been set up to use port I/O if `PCIDMA` is
defined, or has been set up to use memory-mapped I/O if `PCIDMA` is not
defined.

The changes make it possible to build the ni_pcimio module even if the
port I/O functions have not been declared.  (The ni_atmio and ni_mio_cs
modules do still require the port I/O functions to be declared.)

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/20230913170712.111719-10-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>