non barrier versions of dma_map functions

[adharmap at codeaurora.org]

We have a situation where we need to dma map multiple cached buffers for a
single dma transaction.

The current DMA api suggests the use of dma_map_single for cache
consistency. On ARMv7 it performs the necessary cache-operations and calls
data sync barrier instruction (DSB). In our case we would be executing
multiple DSB instruction before starting the dma operation - we need
memory to be consistent only after we map the last buffer.

I am thinking we could define "no barrier" version's of all the mapping
functions and then a barrier function that results in DSB before the dma
is started.

Requesting alternative ideas or code design to get the desired nonbarrier
versions of the mapping functions.

Abhijeet Dharmapurikar