media: atomisp: ov2680: Drop custom ATOMISP_IOC_S_EXPOSURE support

Exposure and gain control should use standard v4l2 controls,
not a custom ioctl.

The next patch in this series will re-add support as standard controls,
this is split into 2 patches for easier reviewing.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>