drm/msm: dpu: Add extra_flush_bits to trigger_flush trace

It's useful to know which bits of the flush come from extra_flush_bits

Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>