PCI: include io.h in pci.h so that ioremap_nocache is defined

Ingo pointed out that the m32r build was broken by pci_ioremap.  It looks like
some files include pci.h w/o including io.h.  The latter defines ioremap_* if
present, so it makes sense to include it in pci.h now that we have pci_ioremap
there.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>