media: Kconfig: move V4L2 subdev API to v4l2-core/Kconfig

This option is part of V4L2 API extra functionality set.
Move it to be at the v4l2-core/Kconfig, where it belongs,
cleaning the main Kconfig file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>