iommu/ipmmu-vmsa: Replace local utlb code with fwspec ids

Now when both 32-bit and 64-bit code inside the driver is using
fwspec it is possible to replace the utlb handling with fwspec ids
that get populated from ->of_xlate().

Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Joerg Roedel <jroedel@suse.de>