i965: Make brw_set_saturate() use stdbool.

i965: Make brw_set_saturate() use stdbool.

There was a chance for brw_wm_emit.c to screw up and pass (1 << 4) instead of
1, which would get converted to 0 when stored.  Instead, use stdbool which
converts nonzero to true/1 like we want.