msm_fb: display: turn off lcdc timing generator when splash is done

The lcdc timing generator is configured by boot loader for splash
screen. TG should be disabled when kernel is about to configure it
with its own parameters. Otherwise, mdp may hang or underrun while TG
is still active.

Change-Id: Ia2b2947c2759975d02e718edf306c86403bc6d33
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>