media: i2c/Kconfig: use sub-menus for I2C support

There are *lots* of I2C ancillary drivers. While we're using
comments to group them, all options appear at the same menu.

It should be a lot clearer to group them into sub-menus, with
may help people to go directly to the driver(s) he's needing
to enable.

Suggested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>