drm/panfrost: Use drm_sched_job_add_syncobj_dependency()

As panfrost_copy_in_sync() performs the same steps as
drm_sched_job_add_syncobj_dependency(), replace the open-coded
implementation in Panfrost in order to simply use the DRM function.

Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209124447.467867-5-mcanal@igalia.com