drm/msm: Cut dpu_kms hooks from msm_pm_suspend/resume

Removes the traces of the non-atomic helper calls in
msm_pm_suspend/resume since we just deleted those functions (see patch
1). Also removes the drm_kms_helper_poll_disable/enable calls, since
the DRM_CONNECTOR_POLL_CONNECT flag is never set so periodic polling
doesn't happen anyways.

v2: reorganized patch order
v3: made error checks less severe

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Bruce Wang <bzwang@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>