i965: Weaken the flushing in gen7_end_transform_feedback().

i965: Weaken the flushing in gen7_end_transform_feedback().

Since 062317d6671 (i965: Go back to using the kernel SOL reset feature.)
we've been flushing the batch on BeginTransformFeedback().  So it's not
necessary to do it on EndTransformFeedback().  A PIPE_CONTROL will work.

This makes gen7_end_transform_feedback() exactly the same as the gen6
variant.  However, they'll diverge again shortly.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>