i965: Move brw_emit_query_begin() to the render ring prelude.

i965: Move brw_emit_query_begin() to the render ring prelude.

Without hardware contexts, the pipeline statistics registers are
free-running and include data from every 3D application running.

In order to find out the contributions of one particular context, we
need to take a snapshot at the start and end of each batch.

Previously, we emitted the PIPE_CONTROL necessary to capture
PS_DEPTH_COUNT when drawing primitives.  Special tracking ensured it
happened only on the first draw of the batch, rather than on every draw.

Moving this to brw_new_batch increases symmetry, since the final
snapshot has always been in brw_finish_batch, which is just a few lines
below.  It should be basically equivalent.

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