ARM: mvebu: remove unneeded ->map_io field for Armada 370/XP

The ->map_io() implementation of Armada 370/XP simply calls
debug_ll_io_init(), which is exactly what the kernel does when
->map_io is NULL. Therefore, there is no need to have a specific
->map_io() implementation in Armada 370/XP.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>