mdss: display: extend mutex coverage inside cmdlist_put

At Current implementation mutex is released after dcs
commands had been added to queue and before cmdlist_commit
called to tx commands. This is created a possibility to allow
other thread do take over command queue and call cmdlist_commit
to tx commands which not added by it. Extend mutex coverage to
including both cmdlsit_put and cmdlist_commit to fix the problem.

CRs-Fixed: 669136
Change-Id: I317adae2b39505d96afe1edd27f1a1ab813b343d
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>