PCI: pciehp: Request control of native hotplug only if supported

[ Upstream commit 408fec36a1ab3d14273c2116b449ef1e9be3cb8b ]

Currently we request control of native PCIe hotplug unconditionally.
Native PCIe hotplug events are handled by the pciehp driver, and if it is
not enabled those events will be lost.

Request control of native PCIe hotplug only if the pciehp driver is
enabled, so we will actually handle native PCIe hotplug events.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>