scripts: extract_dts_includes.py: generate 'compatible' CONFIG flags

Generate CONFIG_DT_COMPAT flags using available nodes
'compatible' property.
Store them in a bogus node_address key of defs dict so
duplicates could be removed.

Signed-off-by: Bobby Noelte <b0661n0e17e@gmail.com>
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>