drm/i915: Don't allow HDCP on PORT E/F

Port E doesn't have HDCP support, and Port F is disabled. Don't setup
the hdcp shim on those.

Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180109185401.16911-1-seanpaul@chromium.org