PNP: Make dev_is_pnp() to be a function and export it for modules

Since we have a dev_is_pnp() macro that utilises the address of the
pnp_bus_type variable, the users, which can be compiled as modules,
will fail to build. Convert the macro to be a function and export it
to the modules to prevent build breakage.

Reported-by: Woody Suwalski <terraluna977@gmail.com>
Closes: https://lore.kernel.org/r/cc8a93b2-2504-9754-e26c-5d5c3bd1265c@gmail.com
Fixes: 2a49b45c

 ("PNP: Add dev_is_pnp() macro")
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>