arm64: dma-mapping: Export arch_setup_dma_ops symbol

Export arch_setup_dma_ops symbol.
Some test modules need to call "arch_setup_dma_ops" to setup
the proper dma operations.

Change-Id: Ieb8aca4dab96ee8bad7c5ad0a47f83e4316bf990
Signed-off-by: Runmin Wang <runminw@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>