Allow the default mode for video peek to be undefined

Forcing the default mode for video peek to be defined to on has broken
use cases for Broadcom devices.

See go/video-peek-legacy-mode for more details.

Bug: 220266078
Test: atest android.media.decoder.cts.DecoderTest
Change-Id: I0a7190c3af0b8ab5ae2f78d8f4df5864efe3b267

headers/media_plugin/media/openmax/OMX_IndexExt.h

@@ -104,6 +104,7 @@ typedef enum OMX_INDEXEXTTYPE {
     OMX_IndexConfigLatency,                         /**< reference: OMX_PARAM_U32TYPE */
     OMX_IndexConfigLowLatency,                      /**< reference: OMX_CONFIG_BOOLEANTYPE */
     OMX_IndexConfigAndroidTunnelPeek,               /**< reference: OMX_CONFIG_BOOLEANTYPE */
+    OMX_IndexConfigAndroidTunnelPeekLegacyMode,     /**< reference: OMX_CONFIG_BOOLEANTYPE */
     OMX_IndexExtOtherEndUnused,
 
     /* Time configurations */