arm: mvebu: armada-xp/37x.dtsi: Sync PCIe DT nodes with Linux v4.20

This patch sync's the PCIe DT nodes with the recent Linux v4.20 version.
This change makes it easier to reference specific PCIe nodes in the
board dts files to e.g. enable a PCIe port as this is now necessary with
the new DM PCI driver for these platforms.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Dirk Eibach <dirk.eibach@gdsys.cc>
Cc: Mario Six <mario.six@gdsys.cc>
Cc: Chris Packham <chris.packham@alliedtelesis.co.nz>
Cc: Phil Sutter <phil@nwl.cc>
Cc: Marek Behún <marek.behun@nic.cz>
Cc: VlaoMao <vlaomao@gmail.com>
Cc: Tom Rini <trini@konsulko.com>