drm/etnaviv: remove generic GPU init failure reporting

The GPU init path now reports any errors which might occur more accurately
than what is possible with the generic "something failed" message.

Remove the generic reporting, so we don't log an error into dmesg anymore
if any of the GPU cores are ignored.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>