Add a mapping for the V4L2_PIX_FMT_NV12 format to PIX_FMT_NV12 for
video4linux2 devices. This is used by Sensoray Model 2253 cards.
Patch by Pete Eberlein (pete AT sensoray DOT com)
Originally committed as revision 24759 to svn://svn.ffmpeg.org/ffmpeg/trunk