PCI: imx6: Fix config read timeout handling

Commit cc7b0d49 ("PCI: designware: Update PCI config space remap
function") made PCI configuration requests non-posted, which means we now
get a synchronous abort when the CFG space read to probe for downstream
devices times out.

Synchronous aborts need to be handled differently from the async aborts we
were getting before, in particular the PC needs to be advanced when
resolving the abort.  This is mostly a copy of what other PCI drivers do on
ARM to handle those aborts.

[bhelgaas: changelog, "Fixes"]
Fixes: cc7b0d49 ("PCI: designware: Update PCI config space remap function")
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>