ACPI / hotplug / PCI: Use pci_device_is_present()

Make the ACPI-based PCI hotplug (ACPIPHP) code use
pci_device_is_present() for checking if devices are present instead
of open coding the same thing.

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