drm/i915: Fix platform coverage for HDCP1.4

HDCP1.4 is enabled and validated only on GEN9+ platforms.

v2:
  Removed the unnecessary parens [Ville]

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1544010283-20223-3-git-send-email-ramalingam.c@intel.com