dma-mapping: Add dma_remap functions

After getting an allocation from dma_alloc_coherent, there
may be cases where it is neccessary to remap the handle
into the CPU's address space (e.g. no CPU side mapping was
requested at allocation time but now one is needed). Add
APIs to bring a handle into the CPU address space again.

Change-Id: Ie92196968c545880f5b9f958ae6a20623ef99bfd
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>