arm64: mvebu: Fix A8K memory mapping and add documentation

Fix the MMU mapping for A8K device family:
 - Separate A7K and A8K memory mappings
 - Fix memory regions by including IO mapping for all
   3 PCIe interfaces existing on each connected CP110 controller
Add A8K memory mapping documentation with all regions
configured by Marvell ATF.

Change-Id: I9c930569b1853900f5fba2d5db319b092cc7a2a6
Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@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>