drm/i915: hdcp_check_link only on CP_IRQ

drm/i915: hdcp_check_link only on CP_IRQ

HDCP check link is invoked only on CP_IRQ detection, instead of all
short pulses.

v3:
  No Changes.
v4:
  Added sean in cc and collected the reviewed-by received.
v5:
  No Change.
v6:
  No Change.
v7:
  No Change.
v8:
  Rebased.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1540286550-20399-3-git-send-email-ramalingam.c@intel.com