media: v4l: Add V4L2-PIX-FMT-Y14P format

This is a packed grey-scale image format with a depth of 14 bits per
pixel. Every four consecutive samples are packed into seven bytes. Each
of the first four bytes contain the eight high order bits of the pixels,
and the three following bytes contains the six least significants bits
of each pixel, in the same order.

As the other formats only needed 5 bytes before, append two bytes in the
documentation array.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>