pci: mvebu: Add PCIe driver for Armada-8K

This patch adds a driver for the PCIe controller integrated in the
Marvell Armada-8K SoC. This controller is based on the DesignWare
IP core.

The original version was written by Shadi and Yehuda. I ported this
driver to the latest mainline U-Boot version with DM support.

Tested on the Marvell DB-88F8040 Armada-8K eval board.

Signed-off-by: Shadi Ammouri <shadi@marvell.com>
Signed-off-by: Yehuda Yitschak <yehuday@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Omri Itach <omrii@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>