drm/i915: Apply Wa_1406680159:icl,ehl as an engine workaround

The register this workaround updates is a render engine register in the
MCR range, so we should initialize this in rcs_engine_wa_init() rather
than gt_wa_init().

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1222
Fixes: 36204d80

 ("drm/i915/icl: Wa_1406680159")
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200311162300.1838847-6-matthew.d.roper@intel.com
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>