Convert pci_delete_child() to a bus_child_deleted() method.

Instead of providing a wrapper around device_delete_child() that the PCI
bus and child bus drivers must call explicitly, move the bulk of the logic
from pci_delete_child() into a bus_child_deleted() method
(pci_child_deleted()). This allows PCI devices to be safely deleted via
device_delete_child().

• Add a bus_child_deleted method to the ACPI PCI bus which clears the device_t associated with the corresponding ACPI handle in addition to the normal PCI bus cleanup.
• Change cardbus_detach_card to call device_delete_children() and move CardBus-specific delete logic into a new cardbus_child_deleted() method.
• Use device_delete_child() instead of pci_delete_child() in the SRIOV code.
• Add a bus_child_deleted method to the OpenFirmware PCI bus drivers which frees the OpenFirmware device info for each PCI device.

This is a stepping stone as part of the PCI-express hotplug patches.
Note that I have not booted powerpc or sparc64 and am still waiting for
a tinderbox build to complete to verify the ofw changes compile.

• Tested booting on amd64 and tested insertion and removal of a cardbus adapter.
• Tested hotplug insertion/removal with out-of-tree PCI-e hotplug patches which tested the ACPI PCI bus case.
• Tested manual deletion of PCI devices via out-of-tree patches to add a 'devctl delete' command.