hw/riscv: Add a new struct RISCVBootInfo

hw/riscv: Add a new struct RISCVBootInfo

Add a new struct RISCVBootInfo to sync boot information between multiple
boot functions.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20241120153935.24706-3-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>