event: Add a script to decode the event-spy list

For debugging and dicoverability it is useful to be able to see a list of
each event spy in a U-Boot ELF file. Add a script which shows this, along
with the event type and the source location. This makes events a little
easier to use than weak functions, for example.

Add a basic sandbox test as well. We could provide a test for other
boards, but for now, few use events.

Signed-off-by: Simon Glass <sjg@chromium.org>

MAINTAINERS

@@ -815,7 +815,9 @@ S:	Maintained
 F:	cmd/event.c
 F:	common/event.c
 F:	include/event.h
+F:	scripts/event_dump.py
 F:	test/common/event.c
+F:	test/py/tests/test_event_dump.py
 
 FASTBOOT
 S:	Orphaned