msm: ADSPRPC: attributes to support per-buffer coherent mappings

Added attributes for forcing a buffer mapped as coherent or
non-coherent by using the DMA_ATTR_FORCE_COHERENT and
DMA_ATTR_FORCE_NON_COHERENT.

Change-Id: Ifecad81dd96b99ab63854bddce378ff775c22d38
Acked-by: Viswanatham Paduchuri <vpaduchu@qti.qualcomm.com>
Signed-off-by: Sathish Ambley <sathishambley@codeaurora.org>