disp: msm: sde: use dma_map_single to flush the buffer

dmac_flush_range api is no longer avaialable on latest kernel.
Use dma_map_single to flush the scm buffer before switching to
higher execution previlege.

Change-Id: Ia1c18a6ab9a9c80f5f9ce79816d9dbd3777474b0
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>