arm: mm: dma-mapping: export arch_setup_dma_ops

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

Change-Id: Icf84c7653743748060d39d08e91175fb4dad3f93
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>