[media] v4l: vb2: add support for shared buffer (dma_buf)

[media] v4l: vb2: add support for shared buffer (dma_buf)

This patch adds support for DMABUF memory type in videobuf2. It calls relevant
APIs of dma_buf for v4l reqbuf / qbuf / dqbuf operations.
For this version, the support is for videobuf2 as a user of the shared buffer;
so the allocation of the buffer is done outside of V4L2. [A sample allocator of
dma-buf shared buffer is given at [1]]
[1]: Rob Clark's DRM:
   https://github.com/robclark/kernel-omap4/commits/drmplane-dmabuf
   [original work in the PoC for buffer sharing]

Signed-off-by: Tomasz Stanislawski <[email protected]>
Signed-off-by: Sumit Semwal <[email protected]>
Signed-off-by: Sumit Semwal <[email protected]>
Acked-by: Laurent Pinchart <[email protected]>
Acked-by: Hans Verkuil <[email protected]>
Tested-by: Mauro Carvalho Chehab <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>