ARM: dts: stih407/410: Tidy up display nodes

The display nodes are common to both STiH407 and STiH410, move them to the
family file.

Acked-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>