pci: Cleanup configuration for pci-hotplug.c

pci-hotplug.c and the CONFIG_PCI_HOTPLUG variable which controls its
compilation are misnamed.  They're not about PCI hotplug in general, but
rather about the pci_add/pci_del interface which are now deprecated in
favour of the more general device_add/device_del interface.  This patch
therefore renames them to pci-hotplug-old.c and CONFIG_PCI_HOTPLUG_OLD.

CONFIG_PCI_HOTPLUG=y was listed twice in {i386,x86_64}-softmmu.make for no
particular reason, so we clean that up too.  In addition it was included in
ppc64-softmmu.mak for which the old hotplug interface was never used and is
unsuitable, so we remove that too.

Most of pci-hotplug.c was additionaly protected by #ifdef TARGET_I386.  The
small piece which wasn't is only called from the pci_add and pci_del hooks
in hmp-commands.hx, which themselves were protected by #ifdef TARGET_I386.
This patch therefore also removes the #ifdef from pci-hotplug-old.c,
and changes the ifdefs in hmp-commands.hx to use CONFIG_PCI_HOTPLUG_OLD.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
