PCI: tango: Add Sigma Designs Tango SMP8759 PCIe host bridge support

This driver is required to work around several hardware bugs in the PCIe
controller.

The SMP8759 does not support legacy interrupts or IO space.

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
[bhelgaas: add CONFIG_BROKEN dependency, various cleanups]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>