PCI: imx6: simplify config access code ...

The PCI core fills in the primary bus number, so there is no
need to walk up the PCI hierarchy in the driver manually.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pci: Add pcie-designware driver ...

Based on the corresponding kernel driver, only small changes
to make it work on barebox.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>