drm/i915/cnl: WaRsUseTimeoutMode

Apparently RC6 residency is lower than expected
with EI mode for most of the cases on CNL A0, B0 and C0.

This Wa doesn't solve our lower residency, but I
believe it is better to have it since EI is not
expected to work by HW engineers anyways.

Cc: David Weinehall <david.weinehall@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170822235828.18322-1-rodrigo.vivi@intel.com