media: atomisp: partially get rid of one abstraction layer

The very same macros are defined as CSS_foo and IA_CSS_foo.

Remove this abstraction, as it just make things confusing,
for no good reason.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>