dt-bindings: mtd: physmap: Ensure all properties are defined

Device specific schemas should not allow undefined properties which is
what 'additionalProperties: true' allows. Add the missing 'ranges'
property, and fix this constraint.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>