intel-iommu: add DMAR table to ACPI tables

Expose Intel IOMMU to the BIOS. If object of TYPE_INTEL_IOMMU_DEVICE exists,
add DMAR table to ACPI RSDT table. For now the DMAR table indicates that there
is only one hardware unit without INTR_REMAP capability on the platform.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: add Intel IOMMU emulation to q35 and add a machine option "vtd" as a switch

Add Intel IOMMU emulation to q35 chipset and expose it to the guest.
1. Add a machine option. Users can use "-machine vtd=on|off" in the command
line to enable/disable Intel IOMMU. The default is off.
2. Accroding to the machine option, q35 will initialize the Intel IOMMU and
use pci_setup_iommu() to setup q35_host_dma_iommu() as the IOMMU function for
the pci bus.
3. q35_host_dma_iommu() will return different address space according to the
bus_num and devfn of the device.

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