[POWERPC] Remove linux,pci-domain properties

The linux,pci-domain property is no longer used by DLPAR/PCI Hotplug
utilites, or LSVPD. This change removes it.

Built for ppc64_defconfig.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>