PCI: dwc: dra7xx: Depend on appropriate SoC or compile test

The PCI controller attached to a SoC isn't much use if the core SoC isn't
enabled, unless of course it's compile testing, so add appropriate
dependency.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>