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.