i915: Fork the shared code from i965.

i915: Fork the shared code from i965.

Of this 15000 lines of code in intel/, we've identified 4000 lines that
are trivially unnecessary for i915, and another 1000 that are pointless for
i965, and expect to find more as time goes on.  Split the i915 driver off,
so that we can continue active development on i965 without worrying about
breaking i915.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Chad Versace <chad.versace@linux.intel.com>
Acked-by: Adam Jackson <ajax@redhat.com>
(and I hear second hand that idr is OK with it, too)