ARM: mvebu: Limit the DMA zone when LPAE is selected

When LPAE is activated on Armada XP, all registers and IOs are still
32bit, the 40bit extension is on the CPU to DRAM path (windows) only.
That means that all the DMA transfer are restricted to the low 32 bits
address space. This is limitation is achieved by selecting ZONE_DMA.

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