i965: Improve conditional rendering in fallback paths.

i965: Improve conditional rendering in fallback paths.

We need to fall back in a couple of cases:
- Sandybridge (it just doesn't do this in hardware)
- Occlusion queries on Gen7-7.5 with command parser version < 2
- Transform feedback overflow queries on Gen7, or on Gen7.5 with
  command parser version < 7

In these cases, we printed a perf_debug message and fell back to
_mesa_check_conditional_render(), which stalls until the full
query result is available.  Additionally, the code to handle this
was a bit of a mess.

We can do better by using our normal conditional rendering code,
and setting a new state, BRW_PREDICATE_STATE_STALL_FOR_QUERY, when
we would have set BRW_PREDICATE_STATE_USE_BIT.  Only if that state
is set do we perf_debug and potentially stall.  This means we avoid
stalls when we have a partial query result (i.e. we know it's > 0,
but don't have the full value).  The perf_debug should trigger less
often as well.

Still, this is primarily intended as a cleanup.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>