drm/i915/gen9: Clean up MOCS table definitions

Use named struct initializers for clarity. Also fix the target cache
definition to reflect its role in GEN9 onwards. On GEN8 a TC value of 0
meant ELLC but on GEN9+ it means the TC and LRU controls are taken from
the PTE.

No functional change, igt/gem_mocs_settings still passing after this
change.

v2: (Chris)
- Add back the hexa literals for the entries.
  Add note that igt/gem_mocs_settings still passes.

CC: Rong R Yang <rong.r.yang@intel.com>
CC: Yakui Zhao <yakui.zhao@intel.com>
CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Zhao Yakui <yakui.zhao@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467380406-11954-2-git-send-email-imre.deak@intel.com