arm: mm: dma-mapping: export arch_setup_dma_ops

Export the arch_setup_dma_ops symbol that can be used by the
dynamically loadable kernel module.

Change-Id: I267a6d23b97be4cb24f236c4d3a2fc90773af94d
Signed-off-by: Qingqing Zhou <qqzhou@codeaurora.org>