i965: Kill software primitive counting entirely.

i965: Kill software primitive counting entirely.

Now that we have hardware contexts, we don't need to continually
reprogram the GS_SVBI_INDEX registers.  They're automatically saved and
restored with the context, so they can just increment over time.  We
only need to reset them when starting transform feedback.

There's also no reason to delay until the next drawing operation; we can
just emit the packet immediately.  However, this means we must drop the
initialization in brw_invariant_state, as BeginTransformFeedback may
occur before the first drawing in a context.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com>