drm/v3d: add multiple syncobjs support

Using the generic extension from the previous patch, a specific multisync
extension enables more than one in/out binary syncobj per job submission.
Arrays of syncobjs are set in struct drm_v3d_multisync, that also cares
of determining the stage for sync (wait deps) according to the job
queue.

v2:
- subclass the generic extension struct (Daniel)
- simplify adding dependency conditions to make understandable (Iago)

v3:
- fix conditions to consider single or multiples in/out_syncs (Iago)
- remove irrelevant comment (Iago)

Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ffd8b2e3dd2e0c686db441a0c0a4a0181ff85328.1633016479.git.mwen@igalia.com