intel-iommu: small fixup with typedef

Separate typedef from struct definitions for vtd_address_space and
intel_iommu_state since it may cause errors with older compilers.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: rename intel_iommu_state to IntelIOMMUState

Rename struct intel_iommu_state to IntelIOMMUState.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: rename vtd_address_space to VTDAddressSpace

Rename struct vtd_address_space to VTDAddressSpace.

Signed-off-by: Le Tan <tamlokveer@gmail.com>