video/hdmi: Add an enum for HDMI packet types

We'll be wanting to send more than just infoframes over HDMI. So add an
enum for other packet types.

TODO: Maybe just include the infoframe types in the packet type enum
      and get rid of the infoframe type enum?

v2: s/AUDIO_CP/ACP/ (Shashank)

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: linux-media@vger.kernel.org
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190110211445.24177-2-ville.syrjala@linux.intel.com