iommu/ipmmu-vmsa: Use fwspec on both 32 and 64-bit ARM

Consolidate the 32-bit and 64-bit code to make use of fwspec instead
of archdata for the 32-bit ARM case.

This is a simplified version of the fwspec handling code from Robin
posted as [PATCH] iommu/ipmmu-vmsa: Convert to iommu_fwspec

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