PCI: Initialize bridge release function at bridge allocation

The introduction of pci_register_host_bridge() kernel interface allows PCI
host controller drivers to create the struct pci_host_bridge object,
initialize it and register it with the kernel so that its corresponding PCI
bus can be scanned and its devices probed.

The host bridge device release function pci_release_host_bridge_dev() is a
static function common for all struct pci_host_bridge allocated objects, so
in its current form cannot be used by PCI host bridge controllers drivers
to initialize the allocated struct pci_host_bridge, which leaves struct
pci_host_bridge devices release function uninitialized.

Since pci_release_host_bridge_dev() is a function common to all PCI host
bridge objects, initialize it in pci_alloc_host_bridge() (ie common host
bridge allocation interface) so that all struct pci_host_bridge objects
have their release function initialized by default at allocation time,
removing the need for exporting the common pci_release_host_bridge_dev()
function to other compilation units.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>