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: NTomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: NSumit Semwal <sumit.semwal@ti.com>
Signed-off-by: NSumit Semwal <sumit.semwal@linaro.org>
Acked-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Tested-by: NMauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

- get rid of ridden V4L2_COMMON symbol

  This symbol is not needed anymore; it can be folded with V4L2
  one, simplifying the Kconfig a little bit;

- Comment why some Kconfig items are needed;

- Remove if test for MEDIA_CAMERA_SUPPORT, replacing it by
  depends on.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

Reorganize the API core changes for them to appear closer to
the items that enable them, and not at the drivers part of
the menu.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

Currently, the v4l2 core is mixed together with other non-core drivers.
Move them into a separate directory.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>