of: implement pci_address_to_pio as weak function

Implement pci_address_to_pio as weak function to remove the dependency on
asm/prom.h. This is in preparation to make prom.h optional.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Grant Likely <grant.likely@linaro.org>

arch/microblaze/include/asm/prom.h

@@ -26,13 +26,4 @@ enum early_consoles {
 
 extern int of_early_console(void *version);
 
-/*
- * OF address retreival & translation
- */
-
-#ifdef CONFIG_PCI
-extern unsigned long pci_address_to_pio(phys_addr_t address);
-#define pci_address_to_pio pci_address_to_pio
-#endif	/* CONFIG_PCI */
-
 #endif /* _ASM_MICROBLAZE_PROM_H */