shmbridge: get bridge mem pool's DMA address with dma_map_single

set up IOMMU mapping for default bridge memory pool and get its
DMA address, thus to address the cache maintenance requirement
when clients suballocate buffer from the pool and pass this buffer
to TZ. Add two APIs to do sync buffer allocated from bridge.

Change-Id: Icd6c70a1185ac96642d9efba74d2b55739eb78ba
Signed-off-by: Zhen Kong <zkong@codeaurora.org>