i965: Combine the two WM pull constant tracked state atoms.

i965: Combine the two WM pull constant tracked state atoms.

These were only split for historical reasons: brw_wm_constants used to
be the "prepare" step, while brw_wm_constant_surface was "emit".  Now
that both happen at emit time, it makes sense to combine them.

Call the newly combined state atom "brw_wm_pull_constants" to indicate
help distinguish it from the Gen6+ atoms that handle push constants.

Finally, remove the BRW_NEW_WM_CONSTBUF dirty bit entirely now that it's
never flagged nor used.

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