hw/riscv/virt-acpi-build.c: Add IMSIC in the MADT

hw/riscv/virt-acpi-build.c: Add IMSIC in the MADT

Add IMSIC structure in MADT when IMSIC is configured.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20231218150247.466427-7-sunilvl@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>