drm/i915/cnl: Cannonlake has 4 planes (3 sprites) per pipe

Issue: VIZ-4525

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: James Irwin <james.irwin@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496781040-20888-6-git-send-email-rodrigo.vivi@intel.com