PCI: dwc: Move GEN3_RELATED DBI definitions to common header

These are common dwc macros that will be used for other platforms.

Link: https://lore.kernel.org/r/1c2d5a7a139be81fa15f356b2380163dbdebdc09.1655799816.git.baruch@tkos.co.il


Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>