i965/skl: Use new MOCS for SKL

i965/skl: Use new MOCS for SKL

On Skylake, the MOCS bits are an index into a table of 63 different,
configurable cache configurations.  As for previous GENs, we only care about
WB and WT, which are available in the documented default set.  Define
SKL_MOCS_WB and SKL_MOCS_WT to the indices for those configucations and use
those for the Skylake MOCS values.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>