Update LIN demo to use lin-config

Changes include:
- Add patch to fix lin-config recipe build QA error.
- Tweak lin-config recipe to install lin_config as executable.
- Rework sllin-demo systemd unit and start_lin_demo.sh script to use
  lin_config with an appropriate configuration file that enables
  polling of the steering wheel adapter instead of just using
  ldattach.

Bug-AGL: SPEC-2918

Change-Id: I3258b7e34cecbbb1cfb93ea6f63a44f0bbb2c06f
Signed-off-by: Scott Murray <scott.murray@konsulko.com>