drm/msm/dpu: Increment vsync_cnt before waking up userspace

The 'vsync_cnt' is used to count the number of frames for a crtc.
Unfortunately, we increment the count after waking up userspace via
dpu_crtc_vblank_callback() calling drm_crtc_handle_vblank().
drm_crtc_handle_vblank() wakes up userspace processes that have called
drm_wait_vblank_ioctl(), and if that ioctl is expecting the count to
increase it won't.

Increment the count before calling into the drm APIs so that we don't
have to worry about ordering the increment with anything else in drm.
This fixes a software video decode test that fails to see frame counts
increase on Trogdor boards.

Cc: Mark Yacoub <markyacoub@chromium.org>
Cc: Jessica Zhang <quic_jesszhan@quicinc.com>
Fixes: 885455d6

 ("drm/msm: Change dpu_crtc_get_vblank_counter to use vsync count.")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Jessica Zhang <quic_jesszhan@quicinc.com> # Trogdor (sc7180)
Patchwork: https://patchwork.freedesktop.org/patch/490531/
Link: https://lore.kernel.org/r/20220622023855.2970913-1-swboyd@chromium.org
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>