hw/riscv: opentitan: Add the flash alias

OpenTitan has an alias of flash avaliable which is called virtual flash.
Add support for that in the QEMU model.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: c9cfbd2dd840fd0076877b8ea4d6dcfce60db5e9.1625801868.git.alistair.francis@wdc.com
2 files changed