compositor,main: use weston_compositor_load_backend()

Move load_backend_new() from main.c to weston_compositor_load_backend()
in compositor.c.

This makes libweston load its own backends without leaking the details
to the user.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Giulio Camuffo <giuliocamuffo@gmail.com>
3 files changed