powerpc/fsl-pci Make PCIe hotplug work with Freescale PCIe controllers

Up to now the PCIe link status on Freescale PCIe controllers was only
checked once at boot time. So hotplug did not work. With this patch the
link status is checked on every config read. PCIe devices not present at
boot time are found after doing 'echo 1 >/sys/bus/pci/rescan'.

Signed-off-by: Rojhalat Ibrahim <imr@rtschenk.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>