[PATCH] powerpc: fix dynamic PCI probe regression

Some hotplug driver functions were migrated to the kernel for use by EEH
in commit 2bf6a8fa.

Previously, the PCI Hotplug module had been changed to use the new
OFDT-based PCI probe when appropriate:
5fa80fcd

When rpaphp_pci_config_slot() was moved from the rpaphp driver to the
new kernel function pcibios_add_pci_devices(), the OFDT-based probe
stuff was dropped.  This patch restores it.

Signed-off-by: John Rose <johnrose@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>