drm/msm: dpu: Move pm_runtime_(get|put) from vblank_enable

There are 4 times that _dpu_crtc_vblank_enable_no_lock() is called:

1- crtc enable
2- crtc disable
3- crtc vblank enable
4- crtc vblank disable

When we enable or disable the crtc, we call drm_crtc_vblank_on and
drm_crtc_vblank_off respectively. That will gate vblank enables and
disables to only being called when the crtc is active. That means that
we can just enable/disable pm runtime in crtc enable/disable. This will
be beneficial in trying to eliminate blocking calls from the vblank call
chain.

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>