WIP:[v4l2]add v4l2 video encoder

This encoder is orignal designed for samsung s5p-mfc encoder
at H.264 format, not done yet.
the codec_data is not need by encoder, remove it the webcamer
could work.
But this encoder encode data would have some screen mess now.
v4l2: add register of gstv4l2videoenc

This code will register gstv4l2videoenc
v4l2: modify the max encoded size

For the encoder of s5p-mfc the size is 2MB, but it is correct
for decoder which is 1MB.
v4l2: modify a debug message

As in this part only allocate buffers but not call STREAMON.
gstv4l2videoenc: correct some metadata
[WIP] v4l2: encoder class

Make the encoder in v4l2 class. Echo format is in its own
class.

Signed-off-by: ayaka <ayaka@soulik.info>
v4l2: modify GstV4l2VideoDecCData to GstV4l2VideoCData
v4l2: add GstVideoCData to v4l2-utils.h

But it broke the code style.
v4l2: video encoder/decoder register
v4l2: fix a bug in min_buffers

There is also V4L2_CID_MIN_BUFFERS_FOR_OUTPUT.