This is in preparation to split the IOMMU device out of the APB. As part of
this commit we also enforce separation of the IOMMU and APB devices by using
a QOM object link to pass the IOMMU reference and accessing the IOMMU registers
via a separate memory region mapped into the APB config space rather than
directly.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Artyom Tarasenko <atar4qemu@gmail.com>