Fix PCIe window decoding on Armada 38x

[mw_semihalf.com]

Summary

Original PCIe nodes for Marvell SoCs consists of ports' nodes
under main controller node. In order to properly parse
this kind of representation in DT a mechanism for traversing
through the tree required an update. Moreover, processing FDT
data consisting of more than 2 cells had to be fixed,
because the 'reg' property of mrvl,pcie node have additional
parameter in front of 64-bit address. It should be skipped
by default. This commit works properly with old mrvl,pcie
representation for Kirkwood and ArmadaXP SoCs.