drm/msm: rename msm_pm_prepare/complete to note the KMS nature

Rename the msm_pm_prepare() and msm_pm_complete() to
msm_kms_pm_prepare() and msm_kms_pm_complete() consequently.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/561646/


Signed-off-by: Rob Clark <robdclark@chromium.org>