drm/i915/icl: WaAllowUMDToModifyHalfSliceChicken7

Required to dinamically set 'Trilinear Filter Quality Mode'
Userpsace consumer is mesa.

V2: Rebase
V3: Update commit message

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181030084504.21537-3-radhakrishna.sripada@intel.com