anv: Stop compacting render targets in the binding table

anv: Stop compacting render targets in the binding table

Instead, always emit one entry for every color attachment in the subpass
or one NULL if there are no color attachments.  This will let us adjust
an Ice Lake workaround so we don't get a stall on every draw call.

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>