sparc/PCI: Use correct offset for bus address to resource

sparc/PCI: Use correct offset for bus address to resource

After we added 64bit mmio parsing, we got some "no compatible bridge window"
warning on anther new model that support 64bit resource.

It turns out that we can not use mem_space.start as 64bit mem space
offset, aka there is mem_space.start != offset.

Use child_phys_addr to calculate exact offset and record offset in
pbm.

After patch we get correct offset.

/pci@305: PCI IO [io  0x2007e00000000-0x2007e0fffffff] offset 2007e00000000
/pci@305: PCI MEM [mem 0x2000000100000-0x200007effffff] offset 2000000000000
/pci@305: PCI MEM64 [mem 0x2000100000000-0x2000dffffffff] offset 2000000000000
...
pci_sun4v f02ae7f8: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [io  0x2007e00000000-0x2007e0fffffff] (bus address [0x0000-0xfffffff])
pci_bus 0000:00: root bus resource [mem 0x2000000100000-0x200007effffff] (bus address [0x00100000-0x7effffff])
pci_bus 0000:00: root bus resource [mem 0x2000100000000-0x2000dffffffff] (bus address [0x100000000-0xdffffffff])

-v3: put back mem64_offset, as we found T4 has mem_offset != mem64_offset
     check overlapping between mem64_space and mem_space.
-v7: after new pci_mmap_page_range patches.
-v8: remove change in pci_resource_to_user()

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Tested-by: Khalid Aziz <khalid.aziz@oracle.com>
Cc: sparclinux@vger.kernel.org
Orabug: 22855133

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
(cherry picked from commit f296714da83b75783997f8dcfe2a9021ef8fedde)
Signed-off-by: Allen Pais <allen.pais@oracle.com>