No functional changes.

Adjust to comply with dt-schema requirements
and make possible to validate values.
Acked-by: Simon Guinot <simon.guinot@sequanux.org>
Signed-off-by: David Heidelberg <david@ixit.cz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>