iomap: make IOPORT/PCI mapping functions conditional

When CONFIG_PCI is not enabled, CONFIG_EISA=y, and CONFIG_GENERIC_IOMAP=y,
drivers/net/3c59x.c build fails due to a recent small change to
<asm-generic/iomap.h> that surrounds pci_iomap() and pci_iounmap() with
#ifdef CONFIG_PCI/#endif.

Since that patch to iomap.h looks correct, add stubs for pci_iomap() and
pci_iounmap() with CONFIG_PCI is not enabled to fix the build errors.

  drivers/net/3c59x.c:1026: error: implicit declaration of function 'pci_iomap'
  drivers/net/3c59x.c:1038: error: implicit declaration of function 'pci_iounmap'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>