core, configs, tools: Prepare for variable IOMMU register set sizes

core, configs, tools: Prepare for variable IOMMU register set sizes

Introduce a size field to struct jailhouse_iommu and fill it via the
config generator. The information can be retrieved from the ACPI tables
for AMD. On Intel, we need to study the Linux mappings, thus we need to
demand that DMAR is enabled now while retrieving system information.

Based on patches by Valentine Sinitsyn.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>