ARM: mvebu: Fix ranges entry on XP GP board

With the latest device tree reorganization which introduced the
'internal-reg' node, now the only region translated is the internal register's.
This makes the description of the hardware incomplete, for it lacks the
Device Bus childs address space.

In order to fix this, it's required to add a 'ranges' entry with a suitable
address space to map Device Bus childs, on a per-board basis.
This patch fixes the ranges property on the Armada XP GP board.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>