scripts: gen_defines: augment edtlib nodes

Add additional attributes to each edtlib.Node we process, before
calling into the write_foo() routines.

This includes the identifier returned by node_ident(), which is used
as the primary identifier for the node, as well as lists for instance
and aliases nodes, and a catchall list that contains all the other
identifiers in addition to the primary one.

Use this information in a new for_each_ident(node, ident) def that
will be put to use in the various write_foo() routines.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>