Move the fdt_valid function to fdt_support.
This changes allow to be able to test the validity of a devicetree in
other c files.
Update code syntax.
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>