Since the libretech-all-h3-cc can use either the H2+, H3 or H5, move the
content of the dts file to a common dtsi file to be included by the H3
variant and in a following patch the H5 variant.

By the way, update the SPDX licence tag position.
Suggested-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>