Convert CONFIG_HOTPLUG_PCI from tristate to bool.  This only affects
the hotplug core; several of the hotplug drivers can still be modules.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NYinghai Lu <yinghai@kernel.org>