mdss: mdp3: Flush fences on dma stop

If during dma stop, we detect that dma
done interrupt was blocked, we flush out
any waiting activity, that includes fb
release fence signaling.

Change-Id: I12a2a43aa22a0fb6546d5e4c7482b6bdbbc2d5b0
Signed-off-by: Animesh Kishore <animeshk@codeaurora.org>