ruvm 0.4.6

This patch is all M6 and finishes the Arm boards. arm virt gets ACPI and the SMMUv3, and there is a new sbsa-ref board.

For M6: arm virt builds QEMU's ACPI tables, so EDK2 can boot Linux from pflash with tables that are byte for byte the same as QEMU 11.1's, with acpi=, spcr=, x-oem-id and x-oem-table-id (#182). On the way this fixed a hang where EDK2 put a legacy virtio I/O BAR at port 0, which QEMU allows on virt and ruvm didn't. riscv virt needed the same fix (#183). arm virt also has the SMMUv3 with -M virt,iommu=smmuv3, with stage 1, stage 2 and nested walks, the command and event queues and the IOTLB, and PCI DMA and MSIs go through it as on QEMU (#184). The device tree and the IORT match QEMU's. The new -M sbsa-ref board ports hw/arm/sbsa-ref.c with its flashes, GICv3 and ITS, SMMUv3, PCIe, sysbus AHCI, PL061 GPIO with the power button, generic watchdog and sbsa-ec (#185). Trusted Firmware and EDK2 boot on it, and the serial log matches QEMU's line for line apart from the Tianocore banner. The GICv3 gains its virtual CPU interface and target-arm gains the PMUv3 registers, so arm virt now has a PMU node in its device tree like QEMU (#186). There is no xHCI, e1000e or bochs-display on sbsa-ref yet, and the default CPU is neoverse-n1 because neoverse-n2 isn't modelled.