mdss: mdp3: turn off panel before turning off dma

There was a flicker during bootloader to kernel transition.
Problem was that we were turing off dma before turning off panel.

Change-Id: I44a0fc9810891293b4b866558b88afaf65ab942d
Signed-off-by: Terence Hampson <thampson@codeaurora.org>
fix mismerge of "msm: mdp3: implement overlay prepare ioctl for mdp3 driver"