i965: Set Broadwell MOCS values everywhere it's possible.

i965: Set Broadwell MOCS values everywhere it's possible.

This patch introduces two pre-canned MOCS values: BDW_MOCS_WB
(write-back, all caches) and BDW_MOCS_WT (write-through, all caches).

We use write-through caching for render targets, and write-back for
all other data.  (At least on Haswell, I believe write-back LLC/eLLC
didn't work for scan-out buffers, while write-through did.)

No performance analysis has been done on the impact of this patch.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Eric Anholt <eric@anholt.net>