bcm2835: add v4l2 camera device

- Supports raw YUV capture, preview, JPEG and H264.
- Uses videobuf2 for data transfer, using dma_buf.
- Uses 3.6.10 timestamping
- Camera power based on use
- Uses immutable input mode on video encoder

Signed-off-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Luke Diamand <luked@broadcom.com>