freedreno/a6xx: Fix primitive counters again

freedreno/a6xx: Fix primitive counters again

We use one mechanism for (REG_A6XX_RBBM_PRIMCTR_8_LO)
PIPE_QUERY_PRIMITIVES_GENERATED, which counts all primitives that exit
the geometry pipeline, whether or not xfb is on.  Then for
PIPE_QUERY_PRIMITIVES_EMITTED, we use the CP_EVENT_WRITE subfunction
that writes out per-stream counts for generated and emitted, but only
when xfb is enabled.

Signed-off-by: Kristian H. Kristensen <hoegsberg@google.com>
Acked-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Rob Clark <robdclark@gmail.com>