ACPI: simplify acpiphp driver with new helper functions

Use the new helper functions introduced previously to simplify the
ACPI-based PCI hotplug (acpiphp) driver.

[rjw: Changelog]
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>