i965: Respect the no_8 flag on Gen6, not just Gen7+.

i965: Respect the no_8 flag on Gen6, not just Gen7+.

When doing repclears, we only want to use the SIMD16 program, not the
SIMD8 one.  Kristian added this to the Gen7+ code, but apparently we
missed it in the Gen6 code.  This patch copies that code over.

Approximately doubles the performance in a clear microbenchmark from
mesa-demos (clearspd -width 500 -height 500 +color) on Sandybridge.

Cc: "10.4 10.3" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>
References: https://code.google.com/p/chrome-os-partner/issues/detail?id=34681