hw/riscv/virt.c: Make block devices default to virtio

hw/riscv/virt.c: Make block devices default to virtio

RISC-V virt is currently missing default type for block devices. Without
this being set, proper backend is not created when option like -cdrom
is used. So, make the virt board's default block device type be
IF_VIRTIO similar to other architectures.

We also need to set no_cdrom to avoid getting a default cdrom device.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240620064718.275427-1-sunilvl@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>