Modified deepstream-test1 to use a GMSL camera to display a green screen and could not display it properly

IIf this camera is supported by v4l2src, please refer to this FAQ.

The pipeline is like this:

v4l2src --> 'video/x-raw, format=UYVY, width=xxx, height=xxx, framerate=xxx/1'  --> nvvideoconvert --> 'video/x-raw(memory:NVMM),format=NV12' --> nvstreammux --> ....

Please first ensure that the v4l2 camera displays correctly when using nv3dsink.