tmf: Add support for custom event type by text line or XML element

tmf: Add support for custom event type by text line or XML element

The text line or XML element can have an associated event type that will
override the definition name as the default event type.

If a custom event field or attribute is defined to set the event type,
it will override that default.

Change-Id: I9e38a0cdb5dc1b4442ca8028bbbbee220dc6001c
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/75892
Reviewed-by: Hudson CI