With support for depth mode gone there really is no need to support
streaming from 2 sensors at once. As discussed and acked on the list
(see Link tag) it is desirable to drop support for this since it
involves quite a lot of special handling / hacks in the code.

This initial commit limits itself to a minimum set of changes to switch
to 1 struct atomisp_sub_device / 1 stream. Further commits will actually
remove / cleanup much of the special handling.

Likewise this initial commit also deliberately skips the opportunity to
turn some multi-line statements into single-line statements, so as to
keep the diff small / easier to review.

Link: https://lore.kernel.org/linux-media/5309d845-063b-6dd9-529d-0f82654290f2@redhat.com/Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>