drm/exynos: don't do any DPMS operation while updating planes

DPMS only makes sense when the mode changes, for plane update changes do
not perform any dpms operation.

This move places the win_commit() and commit() calls directly in the code
instead of calling exynos_drm_crtc_commit() thus avoiding DPMS operations.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>