powerpc: Fix PCI in Holly device tree

The PCI bridge on the Holly board is incorrectly represented in the
device tree.  The current device tree node for the PCI bridge sits
under the tsi-bridge node.  That's not obviously wrong, but the PCI
bridge translates some PCI spaces into CPU address ranges which were
not translated by the "ranges" property in tsi-bridge node.

We used to get away with this problem because the PCI bridge discovery
code was also buggy, assuming incorrectly that PCI host bridge nodes
were always directly under the root bus and treating the translated
addresses as raw CPU addresses, rather than parent bus addresses.
This has since been fixed, thus breaking Holly.

This could be fixed by adding extra translations to the tsi-bridge
node, but this patch instead moves the Holly PCI bridge out of the
tsi-bridge node to the root bus.  This makes the tsi-bridge node
represent only the built-in IO devices in the bridge, with a
more-or-less contiguous address range.  This is the same conventio...