media: atomisp: Remove a bunch of unused atomisp_css_*() functions

Remove various unused atomisp_css_*() functions from
atomisp_compat_css20.c.

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>