sparc64: fix pci_iounmap() when CONFIG_PCI is not set

Guenter reported [1] that the pci_iounmap() changes remain problematic,
with sparc64 allnoconfig and tinyconfig still not building due to the
header file changes and confusion with the arch-specific pci_iounmap()
implementation.

I'm pretty convinced that sparc should just use GENERIC_IOMAP instead of
doing its own thing, since it turns out that the sparc64 version of
pci_iounmap() is somewhat buggy (see [2]). But in the meantime, this
just fixes the build by avoiding the trivial re-definition of the empty
case.

Link: https://lore.kernel.org/lkml/[e-mail]/ [1]
Link: https://lore.kernel.org/lkml/CAHk-=[e-mail]/ [2]
Reported-by: Guenter Roeck <[e-mail]>
Cc: David Miller <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/sparc/lib/iomap.c

···
 EXPORT_SYMBOL(ioport_map);
 EXPORT_SYMBOL(ioport_unmap);
 
+#ifdef CONFIG_PCI
 void pci_iounmap(struct pci_dev *dev, void __iomem * addr)
 {
 	/* nothing to do */
 }
 EXPORT_SYMBOL(pci_iounmap);
+#endif