drm/exynos: Consolidate suspend/resume

drm/exynos: Consolidate suspend/resume

Remove all of the pm_ops from the various platform devices and move to a
consolidated suspend/resume process from the drm driver. This allows us
to properly order operations when we suspend/resume. It also makes the
dpms tracking in exynos_drm_encoder meaningful.

BUG=None
TEST=Tested with/without hdmi & idle/lid suspend/resume. No regressions.

Change-Id: I25bab3843c87960416b1218a48c60c5124404aff
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/37642
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>