of/address: merge of_address_to_resource()

Merge common code between PowerPC and Microblaze.  This patch also
moves the prototype of pci_address_to_pio() out of pci-bridge.h and
into prom.h because the only user of pci_address_to_pio() is
of_address_to_resource().

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Michal Simek <monstr@monstr.eu>
CC: Stephen Rothwell <sfr@canb.auug.org.au>