drm/vc4: Remove BOs seqnos

`bo->seqno`, `bo->write_seqno`, and `exec->bin_dep_seqno` are leftovers
from a time when VC4 didn't support DMA Reservation Objects. Before DMA
Resv was introduced, tracking the correspondence between BOs and jobs
through the job's seqno made sense.

However, this is no longer needed, as VC4 now supports DMA Reservation
Objects and attaches the "job done" fence to the BOs. Therefore, remove
the BOs seqnos in favor of using DMA Resv Objects.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241220134204.634577-4-mcanal@igalia.com