dts: gen_defines.py: Rename *_dev() to *_node()

out_dev(), etc., as a name is a holdover from before commit 73ac1466
("scripts: edtlib: Call nodes "nodes" instead of "devices""). It's
confusing for the same reasons as mentioned in that commit.

Renamings:

 - dev_ident()            -> node_ident()
 - out_dev()              -> out_node()
 - out_dev_s()            -> out_node_s()
 - dev_aliases()          -> node_aliases()
 - dev_path_aliases()     -> node_path_aliases()
 - dev_instance_aliases() -> node_instance_aliases()

Also clean up comments to talk about nodes instead of devices where it
makes sense.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>