drm/atomic: Allow userspace to use damage clips with async flips

Allow userspace to use damage clips with atomic async flips. Damage
clips are useful for partial plane updates, which can be helpful for
clients that want to do flips asynchronously.

Fixes: 0e26cc72 ("drm: Refuse to async flip with atomic prop changes")
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20240702212215.109696-2-andrealmeid@igalia.com