davinci: davinci.c: add comment to XDM 1.0 only option

Mark in modules/codec/davinci.c the CBR option as being available from XDM 1.0 onwards.

modules/codec/davinci/davinci.c

@@ -82,6 +82,7 @@
 #define ENC_QUALITY_LONGTEXT N_( "Encoder qualtiy setting preset. " \
     "ranges from 0..3 (0=encoders default, 1=high quality, 2=speed, 3=user defined" )
 
+/* XDM 1.0 */
 #define ENC_CBR_TEXT N_("Constant bitrate encoding (default: true)" )
 #define ENC_CBR_LONGTEXT N_( "Use constant bitrate encoding. If disabled, " \
     "then variable bitrate encoding is used resulting in higher bandwidth savings." )