arm: move arm_dma_limit to setup_dma_zone

arm: move arm_dma_limit to setup_dma_zone

Since 4dcfa600 ("ARM: DMA-API: better handing of DMA masks for coherent
allocations") arm_dma_limit_pfn has almost substituted the arm_dma_limit.
The remaining user is dma_contiguous_reserve().  It is also referenced in
setup_dma_zone() to calculate arm_dma_limit_pfn.

Kill the global arm_dma_limit and equip setup_zone_dma with the local one.

Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
Reported-by: Vassili Karpov <av1474@comtv.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>