A new mechanism to probe v4l2 M2M devices was implemented in gst 1.8 series, in
order to get such devices probed we now need to enable v4l2-probe compile option
which upstream decided to keep disabled by default (unfortunately), see [1].
With this feature disabled, it is not possible to get v4l2 M2M device to work in
Gstreamer which is a common use case on many embedded platforms. This patch
enables this new option as soon as v4l2 support is enabled in gstreamer -good.
