media: drivers: media: i2c: don't enable if CONFIG_DRM_I2C_ADV7511=n

CONFIG_DRM_I2C_ADV7511 and CONFIG_VIDEO_ADV7511 bind to the same
platform device, so whichever driver gets loaded first will be used on
the device. So they shouldn't be enabled at the same time.

Rework so that VIDEO_ADV7511 and VIDEO_COBALT depends on
DRM_I2C_ADV7511=n or COMPILE_TEST.

Suggested-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>