media: atomisp: get rid of phys event abstractions

ia_css_dequeue_event() is just an alias to ia_css_dequeue_psys_event(),
and atomisp_css_dequeue_event() do nothing but calling the event
dequeue logic.

Get rid of both abstractions, calling the function directly.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>