intel: Make batch macros for doing BCS_SWCTRL setup.

intel: Make batch macros for doing BCS_SWCTRL setup.

We're going to add more BCS_SWCTRL setup instances soon, and you have to
be careful to have the set and restore atomic with the rendering that's
done, so that our state doesn't leak out to other rendering processes.

v2: Rewrite the patch to have batch begin/advance macros so that magic
    numbers don't get sprinkled around (and so you don't mix up your
    do-I-need-to-reset vs what-do-I-reset-to logic, which I nearly did in
    the next patch when first writing it)

Acked-by: Kenneth Graunke <kenneth@whitecape.org>