iommu/ipmmu-vmsa: Make use of IOMMU_OF_DECLARE()

Hook up IOMMU_OF_DECLARE() support in case CONFIG_IOMMU_DMA
is enabled. The only current supported case for 32-bit ARM
is disabled, however for 64-bit ARM usage of OF is required.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>