checks: Warn on node name unit-addresses with '0x' or leading 0s

Node name unit-addresses should generally never begin with 0x or leading
0s. Add warnings to check for these cases, but only for nodes without a
known bus type as there should be better bus specific checks of the
unit address in those cases. Any unit addresses that don't follow the
general rule will need to add a new bus type. There aren't any known
ones ATM.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>