[POWERPC] 4xx: Only reset PCIe PHY on 405EX systems when no link is detected

Since the arch/powerpc PCI subsystem now does a complete re-assignment of
the resources, we can move from the unconditional PCIe PHY reset to the
conditional version. Now the PHY is only reset, if no link is established yet.
An additional PHY reset (one is already done in U-Boot) leads to problems
with some Atheros PCIe boards and some HP FPGA PCIe designs.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>