dt-bindings: pinctrl: amlogic,pinctrl-a4: Add missing constraint on allowed 'group' node properties

The "^group-[0-9a-z-]+$" nodes schema doesn't constrain the allowed
properties as the referenced common schemas don't have constraints.
Add the missing "unevaluatedProperties" constraint.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250507215852.2748420-1-robh@kernel.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>