PCI: xgene: Rename xgene_pcie_probe_bridge() to xgene_pcie_probe()

Rename xgene_pcie_probe_bridge() to xgene_pcie_probe() to follow the
convention of other drivers.  No functional change intended.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>