[PATCH] powerpc: fix dynamic PCI probe regression

Some hotplug driver functions were migrated to the kernel for use by EEH
in commit 2bf6a8fa21570f37fd1789610da30f70a05ac5e3.

Previously, the PCI Hotplug module had been changed to use the new
OFDT-based PCI probe when appropriate:
5fa80fcdca9d20d30c9ecec30d4dbff4ed93a5c6

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>