drm/msm/dpu: Remove dpu_kms_pm_suspend/resume

PM resume was crashing during dpu_kms_pm_resume. This patch removes
dpu_kms_pm_suspend/resume so that msm_pm_suspend/resume uses the atomic
helpers instead (see next patch). This patch also removes
dpu_kms_is_suspend_blocked since it is never called.

v2: Reorganized patches in patchset

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