drm/i915/icl: Wa_1405779004

Disable MSC clock gating to prevent data corruption.

BSpec: 19257

v2: Rebased on top of the WA refactoring
v3: Added References (Mika)
v4:
  - Rebased
  - C, not lisp (Chris)
  - A0 only (Mika)

References: HSDES#1405779004
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/1525814984-20039-10-git-send-email-oscar.mateo@intel.com