linux-imx

drm/sti: implement atomic_check for the planes

Atomic update should never fail. Thus all checks must be done in
the atomic_check function for each plane (gdp, hqvdp and cursor).

Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>