i965: Always enable VF statistics

i965: Always enable VF statistics

Every other unit in the geometry pipeline automatically enables
statistics gathering. This part of the pipe has been controlled by the
DEBUG_STATS variable, but this is asymmetric. This dates back to the
original implementation, and I am not sure if there is a reason for it.

I need access to these stats to implement ARB_pipeline_statistics_query.

Eric wrote it, and Ken touched it last. Do you have any opposition?

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86145
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>