ivi-shell: implement get_screen_from_output

It is an internal API, which returns ivi_layout_screen
for a pregiven weston_output.

Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Wataru Natsume <wnatsume@jp.adit-jv.com>