msm: mdss: enable ulps during suspend for command mode

Enter into ULPS only during suspend for command mode
panel if ulps_suspend flag is enabled in DT.

Change-Id: Ie03fd4c4c59baf7390d7c50e1a9d7727a5e7b06e
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>