hw/riscv/virt.c: support for RISC-V IOMMU PCIDevice hotplug

hw/riscv/virt.c: support for RISC-V IOMMU PCIDevice hotplug

Generate device tree entry for riscv-iommu PCI device, along with
mapping all PCI device identifiers to the single IOMMU device instance.

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241016204038.649340-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>