media: atomisp: ov2680: Rework flip ctrls

Rework the flip ctrls to be more like those of mainline (non staging)
drivers.

This is modelled after the main ov2680 and ov5693 drivers. This also
introduces __ov2680_get_pad_format() to make the ov2680 code more compliant
with the mainline v4l2-subdev APIs.

Note the OV2680_FLIP_REG and OV2680_MIRROR_REG defines are renamed to
OV2680_REG_FORMAT1 and OV2680_REG_FORMAT2 to match the datasheet.

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