ARM: sti: dt: adapt DT to fix probe/bind issues in DRM driver

STI drm drivers probe and bind using component framework was incorrect.
In addition to drivers fix DT update is needed to make all sub-components
become childs of sti-display-subsystem.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>