[media] davinci: add V4L2 dependencies

The davinci media drivers use videobuf2, which they enable through
a 'select' statement. If one of these drivers is built-in, but
the v4l2 core is a loadable modules, we end up with a link
error:

drivers/built-in.o: In function `vb2_fop_mmap':
:(.text+0x113e84): undefined reference to `video_devdata'
drivers/built-in.o: In function `vb2_ioctl_create_bufs':
:(.text+0x114710): undefined reference to `video_devdata'
drivers/built-in.o: In function `vb2_ioctl_reqbufs':
:(.text+0x114ed8): undefined reference to `video_devdata'
drivers/built-in.o: In function `vb2_ioctl_querybuf':
:(.text+0x115530): undefined reference to `video_devdata'

To solve this, we need to add a dependency on VIDEO_V4L2,
which enforces that the davinci drivers themselves can only
be loadable modules if V4L2 is not built-in, and they do
not cause the videobuf2 code to be built-in.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>