hw/riscv/riscv-iommu: parametrize CAP.IGS

hw/riscv/riscv-iommu: parametrize CAP.IGS

Interrupt Generation Support (IGS) is a capability that is tied to the
interrupt deliver mechanism, not with the core IOMMU emulation. We
should allow device implementations to set IGS as they wish.

A new helper is added to make it easier for device impls to set IGS. Use
it in our existing IOMMU device (riscv-iommu-pci) to set
RISCV_IOMMU_CAPS_IGS_MSI.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241106133407.604587-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>