video/hdmi: Introduce helpers for the HDMI vendor specific infoframe

Provide the same programming model than the other infoframe types.

The generic _pack() function can't handle those yet as we need to move
the vendor OUI in the generic hdmi_vendor_infoframe structure to know
which kind of vendor infoframe we are dealing with.

v2: Fix the value of Side-by-side (half), hmdi typo, pack 3D_Ext_Data
    (Ville Syrjälä)
v3: Future proof the sending of 3D_Ext_Data (Ville Syrjälä), Fix
    multi-lines comment style (Thierry Reding)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@gmail.com>