irqchip/apple-aic: Mark aic_info structs __initconst

These structs hold information used only at init time that never
gets modified, hence mark them __initconst.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Suggested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221021235523.76585-1-konrad.dybcio@somainline.org