drm/etnaviv: dump only failing submit

Due to the tracking provided by the scheduler we know exactly which
submit is failing. Only dump this single submit and the required
auxiliary information. This cuts down the size of the devcoredumps
by only including relevant information.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>