kuksa-dbc-feeder-sllin: add recipe

kuksa-dbc-feeder-sllin: add recipe

Add kuksa-dbc-feeder-sllin recipe to install systemd unit and
configuration file to run a second copy of the KUKSA.val DBC
feeder against the demo setup's sllin0 interface.  The systemd
unit will bring up the sllin0 interface by a call to the
can-dev-helper.sh script if run on hardware that lacks the
LIN adapter.  Additionally, the DBC feeder mapping configuration
has been updated with the mappings for the steering wheel LIN
events, and kuksa-dbc-feeder-sllin has been added to the
agl-demo-preload packagegroup for the full AGL demo setup.

Bug-AGL: SPEC-4405

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I360bdf050f75b6a505b5c1748c6216972d5723c1