[media] atomisp: remove sh_css_irq - it contains nothing

We won't be adding abstractions or moving them here so kill it.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>