v4l2: add v4l2 video encoder

This encoder is orignal designed for samsung s5p-mfc encoder
at H.264 format, not done yet.
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.