media: atomisp: ov2680: Drop struct ov2680_resolution / ov2680_res_preview

Drop struct ov2680_resolution and the ov2680_res_preview[] array,
this is now only used in ov2680_enum_frame_size() and only
the width + height are used there.

Replace this with a new struct v4l2_frmsize_discrete ov2680_frame_sizes[]
array.

No functional changes.

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>