meta-crownbay: use gst-va-intel and va-intel and gst-va-mixvideo

Have crownbay use gst-va-intel and va-intel so we can easily test and
make use of the video acceleration capabilities of this machine.

Also have it use the gst-va-mixvideo so the emgd mixvideo components
get selected.

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>