msm: mdss: move pipe to cleanup list if no layer is attached

Commit call should move unassigned pipes to cleanup list before
calling kickoff because it supports "validate + commit"
functionality.

Change-Id: Ia4d690a451b2ba770f285918d46d9118fcaeacce
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>