PCI: Initialize endpoint library before controllers

The endpoint library must be initialized before its users, which are in
drivers/pci/controllers.  The endpoint initialization currently depends on
link order.

This corrects a kernel crash when loading the Cadence EP driver, since it
calls devm_pci_epc_create() and this is only valid once the endpoint
library has been initialized.

Fixes: 6e0832fa ("PCI: Collect all native drivers under drivers/pci/controller/")
Signed-off-by: Alan Douglas <adouglas@cadence.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>