msm: mdss: add support for dma scheduling for dsi v2.1

Dsi controller v2.1 and above supports scheduling of dma
commands. Schedule dsi cmds at the starting of blanking
region to avoid sending of commands in active region
resulting in dsi overflow errors.

Change-Id: I658b7d7008eb9071148820c0ea949ae9ba593ed9
Signed-off-by: Ashish Garg <ashigarg@codeaurora.org>