fakevideosink: Add DMA kind caps into sink template
We need to recognize the DMA kind caps in fakevideosink, which cooperate with !4044 (merged)
then make the pipeline of
gst-launch-1.0 -vf filesrc location=test.265 ! h265parse ! vah265dec ! vapostproc ! "video/x-raw(memory:DMABuf)" ! fakevideosink sync=false
work.