drm/i915: Add DRM Infoframe handling for BYT/CHT

BYT/CHT doesn't support DRM Infoframe. This caused
a WARN_ON due to a missing CASE while executing
intel_hdmi_infoframes_enabled function. This patch
fixes the same.

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1558015817-12025-11-git-send-email-uma.shankar@intel.com