fbdev: msm: Changes for mapping once during dsi on

SMMU buffer mapping/unmapping is done at DSI ON/OFF
instead of doing it during mdss_dsi_cmd_dma_tx to
avoid smmu page faults and NOC errors.

Change-Id: Ie8a80b3076f58eb5918630e603430c4871d6d24f
Signed-off-by: Rashi Bindra <rbindra@codeaurora.org>
Signed-off-by: raghavendra ambadas <rambad@codeaurora.org>