drm/i915: don't warn about Skylake CPU - KabyPoint PCH combo

Apparently there are machines out there with Skylake CPU and KabyPoint
PCH. Judging from our driver code, there doesn't seem to be any code
paths that would do anything different between SunrisePoint and
KabyPoint PCHs, so it would seem okay to accept the combo without
warnings.

Fixes: 22dea0be

 ("drm/i915: Introduce Kabypoint PCH for Kabylake H/DT.")
References: https://lists.freedesktop.org/archives/intel-gfx/2017-February/118611.html
Reported-by: Rainer Koenig <Rainer.Koenig@ts.fujitsu.com>
Cc: Rainer Koenig <Rainer.Koenig@ts.fujitsu.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v4.8+
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1485956769-26015-1-git-send-email-jani.nikula@intel.com