iommu/mediatek: Convert M4Uv1 to iommu_fwspec

Our per-device data consists of the M4U instance and firmware-provided
list of LARB IDs, which is a perfect fit for the generic iommu_fwspec
machinery. Use that directly instead of the custom archdata code - while
we can't rely on the of_xlate() mechanism to initialise things until the
32-bit ARM DMA code learns about groups and default domains, it still
results in a reasonable simplification overall.

CC: Honghui Zhang <honghui.zhang@mediatek.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Honghui Zhang <honghui.zhang@mediatek.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>