msm: mdss: fix command mode panel support for msm8996

Left panel stays in sleep-in mode if clocks are not
turned on for both controllers. Enable clock
before sending commands and skip clamp controller
for command mode panel support on msm8996.

Change-Id: I8d6c6f9253407d1b6fd8001a00be4876a006deea
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>