Fix PCIe window decoding on Armada 38x

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.

Submitted by: Wojciech Macek <wma@semihalf.com>

		Michal Mazur <mkm@semihalf.com>

Obtained from: Semihalf
Sponsored by: Stormshield, Netgate
Differential revision: https://reviews.freebsd.org/D10905