hw/riscv: virt: Move create_fw_cfg() prior to loading kernel

hw/riscv: virt: Move create_fw_cfg() prior to loading kernel

To enable both -kernel and -pflash options, the fw_cfg needs to be
created prior to loading the kernel.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221004092351.18209-3-sunilvl@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>