msm: mdss: move handoff pipes to used list

MDSS client may want to reuse the pipe during
boot up which are currently in use. The pipe
allocation fails when these pipes are in handoff
state and atomic API tries to reallocate them.
Moving them to used list allows client to reuse
them at early stage without waiting for first valid
kickoff.

Change-Id: Ia6f1282ea192e3a0e948488ba833c2580bebb9bf
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>