PCI: imx6: properly shut down core when leaving barebox
As the i.MX6 PCIe core doesn't have a software reachable reset
wired up, it's hard for any driver to get the core into a known
good state.
To make it easier for whatever software follows barebox, bring
back the core into a safe state before leaving barebox.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>