arm: mvebu: theadorable: Set deephasis bit in PCIe configs very early

Testing has shown, that the quality of the PCIe signals and also the
stability of correct link establishment on the 2 PCIe ports is better,
when the deemphasis bit is set in the PCIe config register.

This needs to be done very early, even before the SERDES setup code is
run. This way, the first link will already be established with this
setup.

Signed-off-by: Stefan Roese <sr@denx.de>