drm/msm: dpu: Don't drop locks in crtc_vblank_enable

Now that runtime resume is handled in encoder, we don't need to worry
about crtc_lock recursion when calling pm_runtime_(get|put). So drop the
lock drops in _dpu_crtc_vblank_enable_no_lock().

Changes in v2:
- None

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

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