Philipp Zabel authored Feb 16, 2021 and Derek Foreman committed Sep 28, 2023

In preparation for multi-backend support, add a list of backends to the
weston_compositor structure. Until backends are converted, this list
just contains the single weston_compositor::backend. Keep that pointer
for now, until the conversion is complete.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>