dev: Enable DTB IOMMU binding with a DMA object

dev: Enable DTB IOMMU binding with a DMA object

This happens by storing a iommu reference in the dma device, and by
calling the addIommuProperty method once doing dtb autogeneration for
the device

Change-Id: Ibd585addac686a9eeaba6959f459d81901087549
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20839
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>