anv: Stop setting domains to RENDER on EXEC_OBJECT_WRITE

anv: Stop setting domains to RENDER on EXEC_OBJECT_WRITE

The reason we were doing this was to ensure that the kernel did the
appropriate cross-ring synchronization and flushing.  However, the
kernel only looks at EXEC_OBJECT_WRITE to determine whether or not to
insert a fence.  It only cares about the domain for determining whether
or not it needs to clflush the BO before using it for scanout but the
domain automatically gets set to RENDER internally by the kernel if
EXEC_OBJECT_WRITE is set.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>