v4l2: Add mapping for V4L2_PIX_FMT_YUY32
Documented here:
https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/pixfmt-packed-yuv.html
This formats matches GST_VIDEO_FORMAT_AYUV which is mostly only used by pack/unpack function for generic color convertion, but apparently it's also possible to use this on some IMX hardware (PXP / IPUv3 ?).