intel: Reserve less batchbuffer space.

intel: Reserve less batchbuffer space.

Now that Gen6+ relies on hardware contexts, we don't need to record an
occlusion query value at the end of each batch.  That means we no longer
need to reserve space for the absurd number of PIPE_CONTROLs required to
do that on Sandybridge.

See commit 4e087de51ad0e7ba4a7199d3664e1d096f8dc510, which bumped this
up to 60 bytes.  This is not quite a revert, as it uses 24 bytes instead
of 16, and saves the comments.  As far as I can tell, the old value of
16 bytes was just wrong, so we shouldn't go back to that.

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