media: v4l: omap: add VIDEO_V4L2 dependency

The omap media driver can be built-in while the v4l2 core is a loadable
module. This is a mistake and leads to link errors:

drivers/media/platform/omap/omap_vout.o: In function `omap_vout_remove':
omap_vout.c:(.text+0xec): undefined reference to `v4l2_device_unregister'
omap_vout.c:(.text+0x140): undefined reference to `video_device_release'
omap_vout.c:(.text+0x150): undefined reference to `video_unregister_device'
omap_vout.c:(.text+0x15c): undefined reference to `v4l2_ctrl_handler_free'

An explicit Kconfig dependency on VIDEO_V4L2 avoids the problem.
I ran into this problem for the first time today during my randconfig
builds, but could not find what caused it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>