arm: mach-mvebu: add support for Armada 370 and Armada XP with DT

[ben.dooks@codethink.co.uk: ensure error check on of_property_read_u32]
[ben.dooks@codethink.co.uk: use mpic address instead of bus-unit's ]
[ben.dooks@codethink.co.uk: BUG_ON() if the of_iomap() fails for mpic]
[ben.dooks@codethink.co.uk: move mpic per-cpu register base ]
[ben.dooks@codethink.co.uk: number fetch should use irqd_to_hwirq()]

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Lior Amsalem <alior@marvell.com>
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Yehuda Yitschak <yehuday@marvell.com>
Tested-by: Lior Amsalem <alior@marvell.com>