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>

i.MX6: pci: Avoid aborts when asserting PCIe reset ...

When booting Barebox in the HW environment where PCIe core has been
used but not properly shut down, writing to PCIE_PL_PFLR in
imx6_pcie_assert_core_reset would cause data abort exception.

The problem can be easily reproduced on a i.MX6 based board with PCIe
slot populated with some device by doing:

> bootm -f -e 0x1050 <your board's>.img

Ignoring this exception seem to allow PCIe core to successfully
initialize and enumerate devices properly. This is also how Linux
Kernel version of the driver handles this situation -- it installs
dummy no-op abort handler at the beginning of device's probing.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

i.MX6: pci: Reconcile imx6_pcie_start_link with the kernel code ...

Reconcile imx6_pcie_start_link with almost identical
imx6_pcie_establish_link from analogous Linux kernel driver. This
change is purely cosmetical, but refactoring the code this way
simplifies implementation comparison.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

i.MX6: pci: Replace magic number with a named constant ...

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pci: Add i.MX6 pcie support ...

Based on the corresponding kernel driver with changes to make it
work on barebox.

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