drm/i915/icl: WaModifyGamTlbPartitioning

Adjust default GAM TLB partitioning for performance reasons.

v2: Only touch the bits that we really need
v3: Rebased on top of the WA refactoring
v4:
  - Added References (Mika)
  - Rebased
v5:
  - Rebased
  - C, not lisp (Chris)
  - Correct reference number (Mika)

References: HSDES#220160670
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1525814984-20039-6-git-send-email-oscar.mateo@intel.com