ACPI / hotplug / PCI: Store parent in functions and bus in slots

To avoid chasing more pointers than necessary in some situations,
move the bridge pointer from struct acpiphp_slot to struct
acpiphp_func (and call it 'parent') and add a bus pointer to
struct acpiphp_slot.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

diff --cc drivers/pci/hotplug/acpiphp.h
Simple merge

diff --cc drivers/pci/hotplug/acpiphp_core.c
Simple merge

diff --cc drivers/pci/hotplug/acpiphp_glue.c
Simple merge