drm/i915: II stage HDCP auth for repeater only

Second stage of HDCP authentication required only if the HDCP
sink is a repeater.

This patch imposes above condition on second stage HDCP authentication.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1516254488-4971-3-git-send-email-ramalingam.c@intel.com