drivers: video: Add video_buf_type

M2M devices like ISPs or PxP have two separate buffer queues, i.e.
incoming and outcoming queues. For each API, the driver needs to
distinguish on which queue it needs to take action.

Add video buffer type to support this kind of devices.

- get_caps(), set/get_format(), enqueue()/dequeue(): the buffer type
is embeded in the video_caps, video_format and video_buffer structs

- video_stream_start/stop() : buffer type needs is sent as a parameter

Signed-off-by: Phi Bang Nguyen <phibang.nguyen@nxp.com>