ARM: mvebu: Add MBus to Armada 370/XP device tree

The Armada 370/XP SoC family has a completely configurable address
space handled by the MBus controller.

This patch introduces the device tree layout of MBus, making the
'soc' node as mbus-compatible.
Since every peripheral/controller is a child of this 'soc' node,
this makes all of them sit behind the mbus, thus describing the
hardware accurately.

A translation entry has been added for the internal-regs mapping.
This can't be done in the common armada-370-xp.dtsi because A370
and AXP have different addressing width.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>