make dtbs_check warm about unknown address/size-cells property in the
pinetab device-tree.

This is because these information are not necessary.

Drop them.
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201011211514.155266-1-peron.clem@gmail.com