i965: Make brw_upload_sampler_state_table handle Gen7+ as well.

i965: Make brw_upload_sampler_state_table handle Gen7+ as well.

This copies a few changes from gen7_upload_sampler_state_table; the next
patch will delete that function.

Gen7+ has per-stage sampler state pointer update packets, so we emit
them as soon as we emit a new table for a stage.  On Gen6 and earlier,
we have a single packet, so we delay until we've changed everything
that's going to be changed.

v2: Split 3DSTATE_SAMPLER_STATE_POINTERS_XS packet emission into a
    helper function (suggested by Topi Pohjolainen).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>