mdss: display: initialize panel_mode at mdss_dsi_ctrl_init

Initialize dsi controller's panel_mode at mdss_dsi_ctrl_init()
due to mdss_dsi_host_init() is not called during boot up if
continuous splash is enabled. An unnecessary timeout will happen
for dcs command send of command mode panel if panel_mode is
initialized as video mode.

Change-Id: I041abcebb9479f3d55f2f21d560aced6c4b77b91
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>