mdss: Avoid panel ON commands during boot up for command mode

In command mode, when continuous splash is enabled, we do not
send the panel OFF commands through the SPLASH_BEGIN callback.
Avoid the SPLASH_FINISH callback also for command mode since
panel ON commands are not required to be sent. This avoids
unnecessary warnings during boot up.

Change-Id: Ifc249f259655045ecd799b57e1efb964238c504a
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>