arm: mvebu: add Armada XP SATA support

This patch initializes the SATA address windows on Armada XP and
allows it to work with the existing mvsata_ide driver.
It also adds the necessary configuration for the db-mv784mp-gp board.

Signed-off-by: Anton Schubert <anton.schubert@gmx.de>
Tested-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>