drm/i915/hsw: Set correct Haswell PTE encodings.

The cacheability controls have changed, and the bits have been
rearranged in general.

Note that age 0 is the oldest (most likely to get evicted) and age 3
is the youngest (most likely to stick around for a bit). We've picked
0 for no reason, but atm it shouldn't matter anyway (since we don't
yet try to differentiate between different objects).

v2: Remove comments for snb/ivb cache leves, that's a separate change.

v3: Resolve conflicts due to patch series reordering.

v4: Rebased on top of Kenneth Graunke's ->pte_encode refactoring.

v5: Removed eLLC bits for separate patch.

In the internal repository this was:
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
[danvet: Add comment about cache ages as requested by Ben provoked due
to a question from Damien.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>