MLK-15080 PCI: imx: pcie ep can't be probed properly

MLK-15080 PCI: imx: pcie ep can't be probed properly

iMX7D Sabre SD board implement the GPIO expander
connected to a peripheral bus.
Probe deferral would be triggered when try to request
the expanded GPIO at the first time.
pcie ep can't be probed properly at the second probe,
because of the duplicated registration of the sysfs.

Change the registration point of the sysfs to fix
this issue.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
rebase on v4.19
Signed-off-by: Vipul Kumar <vipul_kumar@mentor.com>