The only supported types are none and PWM. Other values are obsolete or
reserved, don't add them.
Tested-by: NKamal Mostafa <kamal@canonical.com>
Tested-by: NMartin <bugs@mrvanes.com>
Tested-by: jrg.otte@gmail.com
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>