i965: Avoid flushing the batch for every blorp op.

i965: Avoid flushing the batch for every blorp op.

This brings over the batch-wrap-prevention and aperture space checking
code from the normal brw_draw.c path, so that we don't need to flush the
batch every time.

There's a risk here if the intel_emit_post_sync_nonzero_flush() call isn't
high enough up in the state emit sequences -- before, we implicitly had
one at the batch flush before any state was emitted, so Mesa's workaround
emits didn't really matter.  Since the SNB fixes by Ken, I didn't see any
regressions after 3 piglit runs.

Improves cairo-gl performance by 13.7733% +/- 1.74876% (n=30/32)
Improves minecraft apitrace performance by 1.03183% +/- 0.482297% (n=90).
Reduces low-resolution GLB 2.7 performance by 1.17553% +/- 0.432263% (n=88)
Reduces Lightsmark performance by 3.70246% +/- 0.322432% (n=126)
No statistically significant performance difference on unigine tropics
(n=10)
No statistically significant performance difference on openarena (n=755)

The two apps that are hurt happen to include stalls on busy buffer
objects, so I think this is an effect of missing out on an opportune
flush.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>